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COAL 

ITS  COMPOSITION,  ANALYSIS,  UTILIZATION 
AND  VALUATION 


McGraw-Hill  BookCompaiiy 


Electrical  World         The  Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

Railway  Age  G  azette  American  Machinist 

Signal  Engineer  American  Engneer 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chemical  Engineering  Power 


COAL 


ITS  COMPOSITION,  ANALYSIS, 
UTILIZATION  AND  VALUATION 


BY 

E.  E.  SOMEKMEIER 

Professor  of  Metallurgy,  Ohio  State  University 


McGRAW-HILL   BOOK   COMPANY 

239  WEST  39TH  STREET,   NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1912 


OF 

fBANIS  H  . 


D6PI. 


COPYRIGHT,  1912,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY 


THE   SCIENTIFIC    PRESS 

ROBERT    DRUMMONO    AND    COMPANY 

BROOKLYN,  N.  Y. 


37 

t;.;;---j 

DEPi 


PREFACE 


THE  data  and  descriptive  matter  given  herein,  are  largely 
based  upon  private  notes  and  upon  information  and  material 
scattered  through  text-books,  technical  bulletins,  and  in  original 
papers  in  technical  and  scientific  journals.  Much  of  this  data 
is  either  inaccessible  or  in  such  a  form  as  not  to  be  readily 
applied  or  interpreted  arid  hence  i^  not  likely  to  be  utilized 
by  those  who  have  the  most  active  interest  in  coal. 

In  the  preparation  and  arrangement  of  the  material,  three  dis- 
tinct classes  of  readers  have  been  to  a  certain  extent  kept  in  mind : 

(1)  The  mechanical  and  power  plant  engineer; 

(2)  The  chemical  engineer  and  chemist; 

(3)  The  non-technically  trained  business  man  and  operator 
who  has  to  do  with  the  buying  and  selling  of  the  coal. 

In  including  data  which  might  be  of  interest  and  value  to 
these  different  groups  of  readers  a  portion  of  the  material  is 
necessarily  elementary  for  some  and  a  portion  is  correspondingly 
technical  for  others.  Good  advice  to  each  reader  is  to  select 
that  which  may  be  of  interest  and  use,  and  to  pass  over  any 
discussion  or  data  which  may  appear  too  elementary  or  too 
technical  for  his  needs. 

To  the  technical  man  who  is  familiar  with  much  of  the  data 
and  many  of  the  formulas  given,  it  may  appear  that  many  of 
the  simpler  illustrations  and  details  might  perhaps  just  as  well 
have  been  omitted.  However,  it  is  the  writer's  experience  that 
specific  formulas  and  specific  data  are  not,  as  a  rule,  likely  to  be 
given  too  much  in  detail  to  suit  the  occasional  user,  who  may 
have  neither  the  time  nor  the  inclination  to  elaborate  the  formula 
or  to  check  up  the  data.  He  wants  each  in  a  form  easily  under- 
stood and  readily  applicable  to  his  needs. 

In  the  effort  to  meet  this  "  want  "  some  statements  are 
repeated,  perhaps  too  often,  some  details  enlarged  upon  a  little 
too  much  and  a  few  assumptions  made  which  are  perhaps  not 


M127178 


vi  PREFACE 

strictly  in  accordance  with  facts.  It  is  hoped,  however,  that 
any  errors  in  this  direction  are  of  little  real  consequence  and 
that  the  collection  of  material  given  herein  may  be  a  slight  con- 
tribution toward  a  more  general  appreciation  of  the  properties 
and  a  better  utilization  of  one  of  the  earth's  most  valuable  assets 
— coal. 

The  author  desires  to  express  his  appreciation  to  Professor 
E.  A.  Hitchcock  of  the  Department  of  Mechanical  Engineering, 
Ohio  State  University,  and  Professor  D.  J.  Demorest  of  the 
Department  of  Metallurgy,  for  advice  and  suggestions. 

Especial  acknowledgment  is  due  to  the  late  Professor  N.  W. 
Lord,  the  able  and  inspiring  teacher,  to  whom  the  author  is 
indebted  for  much  of  the  material  given  herein. 

E.  E.  SOMERMEIER. 
October,  1912. 


INTRODUCTION 


COAL  is  generally  recognized  as  being  a  product  of  the  more  or 
less  complete  decomposition  of  vegetable  matter  under  varying 
conditions  of  moisture,  temperature  and  pressure.  Depending 
upon  the  varying  conditions  and  upon  the  completeness  of  the 
decomposition  and  upon  the  kind  of  vegetation  from  which  it  is 
derived,  the  resultant  product  as  it  actually  occurs  is  far  from  uni- 
form, ranging  from  the  initial  stage  of  woody  fibrous  peat  through 
lignite  (brown  coal),  bituminous  coal  high  in  oxygen,  bituminous 
coal  low  in  oxygen,  semi-bituminous  coal,  anthracite  and  the  final 
stage — graphite.  For  similar  conditions  of  moisture,  temperature, 
extent  of  decomposition  and  similar  vegetable  origin,  the  resultant 
coal  should  be  uniform  in  composition  and  properties.  Usually, 
however,  other  factors  acting  during  the  period  of  formation 
modify  and  change  the  final  product,  so  that  coal  from  different 
portions  of  the  same  bed  or  even  different  portions  of  the  same 
mine  is  far  from  uniform  in  some  important  properties,  namely, 
the  content  of  sulphur  and  ash. 

If  coal  contained  only  constituents  which  were  present  in  the 
original  vegetable  matter,  it  would  be  uniformly  low  in  both 
sulphur  and  ash,  but  during  the  early  stages  of  its  formation  under- 
neath the  surface  of  swamps  or  lakes,  streams  or  rivulets  carried 
silt  and  sediment  over  the  decomposing  bed  of  vegetation,  which 
sediment  settled  down  and  became  an  integral  but  varying  con- 
stituent of  the  coal.  Sulphur  in  solution  in  the  water,  coming  in 
contact  with  salts  of  iron  and  reducing  organic  compounds  resulted 
in  the  formation  and  precipitation  of  pyrite,  while  other  reactions 
not  clearly  understood  produced  variable  quantities  of  organic 
compounds  of  sulphur  as  a  constituent  of  the  coal. 

Other  factors  or  agencies  may  also  materially  affect  the  coal 
in  certain  portions  of  the  seam  or  field.  Faults  and  fractures  in 
the  coal  and  surrounding  rocks  are  often  accompanied  by  local 
variations  in  the  nature  of  the  coal.  Weathering  of  the  coal  near 

vii 


viii  INTRODUCTION 

the  outcrop  often  causes  that  portion  to  differ  in  quality  from  the 
more  deeply  covered  and  better  protected  portions.  Still  other 
factors  or  agencies  might  be  enumerated  as  causes  for  local  or 
wide-spread  differences  in  the  coal,  but  those  already  given  suffice 
to  show  why  variations  in  properties  and  constituents  are  to  be 
expected  rather  than  the  occurrence  of  a  material  of  uniformity  in 
properties  and  exactness  in  composition. 


CONTENTS 


PAGE 

PREFACE v 

INTRODUCTION vii 


CHAPTER  I 

COMPOSITION  AND  HEATING  VALUE 

Moisture — Ash — Sulphur — Total  heating  value — Heat  produc- 
ing constituents — Calculation  of  heating  value  from  the  chemical 
composition — Practically  available  heating  value — Determination 
of  heat  lost  during  combustion — Calculation  of  heating  value  of 
Hocking  or  Ohio  No.  6  coal — Printed  forms  for  heat  balance — 
Thermal  capacity  table  for  heat  balance  calculation — Comparison 
of  heat  values  on  coal  as  fired  with  the  A.I.M.E.  code — Variation 
in  available  heating  power — Commercial  value  of  coal — Residual 
coal — Calculation  of  heating  value  from  proximate  analysis  and 
from  H. 


CHAPTER  II 

CHEMICAL  ANALYSIS  OF  COAL 43 

Proximate  analysis- — Proximate  analysis  of  different  coals — Dis- 
cussion of  and  constituents  of  proximate  analysis — Ultimate  analysis 
— Calculation  of  ultimate  analysis. 


CHAPTER  III 

SAMPLING 57 

Mine  sampling — Car  sampling  and  sampling  coal  as  used — Reduc- 
tion of  large  samples — Effects  of  slate  and  pyrite  on  sample — Effects 
of  clean  coal  on  sample — Relation  of  car  sample  to  number  of  samples 
—Treatment  of  the  sample  in  the  chemical  laboratory — Special 
notes  on  sampling. 

ix 


x  CONTENTS 

CHAPTER  IV 

PAGE 

METHODS  OF  ANALYSIS 79 

Moisture — Ash — Volatile   matter — Fixed   carbon — Sulphur — 
Ultimate  analysis — Nitrogen — Phosphorus — Oxygen . 


CHAPTER  V 

DETERMINING  THE  CALORIFIC  VALUE 91 

Description  of  the  determination — Special  notes  on  the  deter- 
mination— Complete  combustion  of  the  sample — Valve  leakage — 
Water  used — Temperature  conditions — Acidity  corrections — Correc- 
tion for  nitric  acid — Correction  for  sulphuric  acid — Ignition  of  wire 
— Cutting  down  voltage  by  means  of  a  resistance  coil — Heat  devel- 
oped with  closed  circuit — Effect  of  the  coil  on  the  heat  developed — 
Water  equivalent  of  the  calorimeter — Heat  of  combustion  of  standard 
substances — Errors  in  graduation  of  thermometers — Determination 
of  graduation  errors  by  divided  threads — Determination  of  gradua- 
tion errors  by  comparison  with  a  standard  thermometer — Determina- 
tion of  graduation  errors  by  experimental  determinations  at  different 
temperatures  with  materials  of  known  heating  value — Stem  tem- 
perature correction — Use  of  tables  in  determination  of  steam  tem- 
perature correction — Correction  for  variations  in  the  specific  heat 
of  water — Effect  of  hydrogen  in  the  sample  on  the  observed  calorific 
value — Use  of  a  cover  on  the  calorimeter — Oxygen  impurities. 


CHAPTER  VI 
SUMMARY  OF  CHEMICAL  DETERMINATIONS  OR  RECORDS 119 

CHAPTER  VII 

IMPROVEMENT  OF  COAL  BY  WASHING 122 

Method  of  operation — Typical  results. 

CHAPTER  VIII 

PURCHASE  OF  COAL  UNDER  SPECIFICATIONS 126 

Total  heating  value  an  index  of  the  commercial  value — Other 
factors  affecting  the  commercial  value — Advantages  of  purchase 
of  coal  under  specifications — Drawing  up  specifications — Points  to 
be  considered — Reports  from  cities  purchasing  coal  under  specifi- 
cations. 


CONTENTS  xi 

CHAPTER  IX 

PAGE 

FLUE  GAS  ANALYSIS 132 

Composition  of  flue  gas — Analysis  of  the  gas — Sampling  the  gas — 
Aspiration  of  the  gas — Apparatus  for  making  the  analysis — Opera- 
tion of  the  Orsat  apparatus — Reagents  used  and  preparation — 
Filling  the  Orsat  apparatus — Absorbing  power  of  reagents — Care  of 
apparatus — Discussion  and  interpretation  of  Orsat  results — Errors 
in  the  Orsat  determination — Alternation  of  samples  on  standing — 
Leakage — Chemical  alteration — Alteration  of  samples  by  absorp- 
tion in  water — Effect  of  a  water  seal  upon  samples. 

CHAPTER  X 

ANALYTICAL  TABLES 158 

Composition  of  different  fuels — Composition  and  heating  value 
of  coals  of  the  United  States  arranged  alphabetically  by  states. 

INDEX..  .   169 


COAL 


CHAPTER  I 
COMPOSITION  AND  HEATING  VALUE 

CONSIDERED  from  a  practical  point  of  view,  coal  may  be 
described  by  discussing  some  of  the  more  or  less  common  terms 
used  in  connection  with  its  composition,  analysis  and  utilization, 
some  of  which  are  as  follows: 

(a)  Moisture. 

(6)  Ash. 

(c)  Sulphur. 

(d)  Heating  value,  total  and  practically  available. 

(e)  "Residual  coal/'  that  is,  coal  free  from  the  variable  factors 
— moisture,  ash  and  sulphur. 

(/)  Proximate  analysis,  in  which  the  composition  is  expressed 
as  percentage  of  moisture,  volatile  matter,  fixed  carbon  and  ash 
present. 

(g)  Ultimate  analysis,  in  which  the  composition  is  given  in 
percentage  of  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur  and 
ash. 

MOISTURE 

The  term  moisture  includes  only  the  more  or  less  loosely  held 
water  which  is  driven  off  by  heating  the  finely  powdered  coal 
slightly  above  the  boiling-point  of  water,  about  105°  C.  or 
220°  F.  The  residual  coal  substance  or  the  mineral  matter 
present  in  the  ash  may  hold  additional  water  which  is  given 
up  on  heating  to  higher  temperatures,  while  still  more  water  is 
produced  upon  the  actual  combustion  of  the  coal.  But  in  the 
ordinary  use  of  the  term  "  moisture,"  this  more  closely  held  water 

1 


2  NOTES  ON  COAL 

or  the  water  produced  by  burning  of  the  fuel  is  never  included, 
and  if  the  closely  held  water  is  given  at  all  in  an  analysis  it  is 
designated  "  combined  water  "  or  "  water  of  combination. " 

The  amount  of  moisture  in  coal  is  variable,  depending  upon 
the  nature  of  the  coal,  upon  its  physical  condition  (degree  of 
fineness)  and  upon  weather  conditions.  As  mined,  Ohio  coals 
contain  from  4  to  10  per  cent  of  moisture.  If  allowed  to  air  dry 
a  large  portion  of  this  moisture  is  expelled  and  well  air-dried 
samples  of  Ohio  coals  crushed  to  J  inch  and  finer  usually  contain 
less  than  3  per  cent  of  moisture.  On  the  other  hand,  the 
amount  of  loosely  held  moisture  retained  by  fine  coal  (slack)  may 
be  quite  large.  A  car  of  slack  which  has  been  rained  upon  may 
contain  as  much  as  15  to  20  per  cent  of  moisture,  a  large  part  of 
this,  as  much  as  10  to  15  per  cent,  being  what  may  be  termed 
"  surface  "  moisture  or  the  moisture  which  gives  the  wet  appear- 
ance to  the  slack.  On  the  other  hand,  lump  coal  containing 
little  or  no  slack  retains  a  comparatively  small  amount  of  surface 
moisture.  Egg  and  lump  coal  from  a  washer,  if  allowed  to  drain 
thoroughly,  does  not  hold  over  2  or  3  per  cent  of  moisture  as 
superficial  or  surface  moisture. 

However,  apparently  dry  lump  coal  often  contains  a  con- 
siderable amount  of  moisture.  Lump  coal  gives  up  moisture 
very  slowly  to  air,  and  it  is  probable  that  most  shipments  of 
lump  coal  from  Ohio  mines  contain  4  or  5  per  cent  of  moisture 
upon  delivery  even  in  dry  summer  weather,  while  in  winter  the 
amount  in  the  lump  coal  as  delivered  is  practically  the  same  as 
when  mined,  which  in  some  Ohio  coals  is  as  high  as  8  or  10  per 
cent.  Shipments  of  slack  made  in  dry  summer  weather  lose 
considerable  moisture  in  transit  and  may  contain  several  per 
cent  less  moisture  on  arrival  at  the  point  of  destination  than 
when  shipped  from  the  mine,  while  in  wet  weather  the  reverse 
is  likely  to  be  true,  the  shipment  containing  more  moisture  than 
when  loaded  at  the  mine. 

The  statement  regarding  moisture  in  Ohio  coals  applies  in 
general  to  coals  of  intermediate  moisture  content.  Under  similar 
conditions,  for  many  West  Virginia  coals  the  values  are  lower; 
for  Illinois,  Indiana  and  Iowa  coals,  the  values  are  somewhat  higher 
than  those  given  for  the  Ohio  coals,  while  in  the  case  of  lignites 
the  moisture  is  very  much  higher,  40  per  cent  and  over  as  mined, 
and  10  to  15  per  cent  in  the  air-dried  lignite. 


COMPOSITION  AND  HEATING  VALUE  3 

Unless  special  precautions  are  taken  to  prevent  moisture  loss 
during  handling,  the  percentage  of  moisture  in  the  sample  analyzed 
may  be  considerably  lower  than  in  the  coal  as  mined  or  shipped, 
and  the  specimen  analyses  exhibited  by  the  operator  giving  the 
analysis  of  his  coal  are  in  many  cases  lower  in  moisture  than  the 
average  of  the  coal  which  is  received  by  the  consumer. 

ASH 

The  term  "  Ash/'  as  commonly  used,  means  the  ignited  mineral 
residue  left  after  complete  combustion  or  burning  of  the  coal.  This 
residue  consists  essentially  of  the  mineral  matter  inherent  in  the 
coal  and  varying  quantities  of  slate  and  clay  from  the  roof  or  floor 
of  the  mine  or  from  partings  in  the  seam  itself,  also  oxide  of  iron 
from  the  combustion  of  pyrite  which  may  be  present  in  the  coal. 
If  the  ash  contains  little  iron  it  is  light  colored,  usually  highly 
silicious  and  gives  little  trouble  on  the  grate  bars.  If  it  contains 
much  iron  it  is  reddish  and  may  give  trouble  from  clinkering. 
As  ordinarily  reported  the  ash  represents  the  actual  weight  of 
mineral  residue  after  the  coal  is  entirely  burned. 

Corrected  ash.  Some  chemists  report  "  corrected  ash," 
which  correction  is  based  on  the  following  points  and  reasoning: 
Iron  as  it  occurs  in  coal  is  usually  present  as  pyrite,  a  combination 
of  iron  and  sulphur  of  which  more  will  be  said  under  the  head  of 
"  Sulphur."  In  burning  the  coal  the  iron  unites  with  oxygen  from 
the  air  and  remains  in  the  ash  as  oxide  of  iron  and  weighs  more 
than  the  iron  present  in  the  original  coal.  One  gram  of  iron  when 
oxidized  to  ferric  oxide  weighs  1.43  grams.  This  one  gram  of  iron 
if  present  as  pyrite  is  combined  with  1.14  grams  of  sulphur,  and 
as  the  chemist  does  not  as  a  rule  determine  the  iron,  but  does  de- 
termine the  sulphur  in  making  the  corrected  ash  reports,  he  bases 
the  amount  of  the  correction  upon  the  amount  of  sulphur  present 
and  deducts  three-eights  of  the  amount  of  sulphur  from  the 
weight  of  ash  as  actually  weighed.  A  correction  made  on  this 
basis  is  always  too  large  and  in  some  cases  may  be  decidedly  too 
high  as  some  of  the  sulphur,  sometimes  as  much  as  2  per  cent,  is 
present  as  organic  sulphur  and  hence  has  no  iron  combined  with 
it.  Again  some  of  the  iron  may  be  actually  present  in  an  oxidized 
form  and  hence  need  no  correction.  Furthermore,  the  mineral 
matter  in  the  coal  present  as  slate  or  clay  upon  ignition  lores 


COAL 


approximately  15  per  cent  of  combined  water,  hence  the  weight  of 
ash  derived  from  this  source  is  lower  than  the  amount  of  mineral 
matter  originally  present,  the  amount  being  about  0.17  of  one 
per  cent  4for  each  per  cent  of  ash  derived  from  clay  and  shale. 
Hence  if  the  object  of  a  "  corrected  ash  "  is  to  obtain  a  correct 
combustible  residue,  the  correction  should  also  include  this  cor- 
rection due  to  changes  in  weight  in  clay  and  shale,  which  is  directly 
opposite  in  its  effect  upon  ash  to  the  corrections  made  for  oxida- 
tion of  iron.  The  loss  in  weight  from  the  ignition  of  about  2 \  per 
cent  of  clay  equals  the  increase  in  the  weight  of  ash  due  to  the 
oxidation  of  thejron  equivalent  to  1  per  cent  of  sulphur  present 
as  pyrite.  The  amounts  of  clay  and  slate  present  are  often  two  or 
three  times  as  high  as  the  amount  of  iron  present  as  pyrite.  Car- 
bonate and  sulphate  of  calcium  are  sometimes  present  as  a  part 
of  the  mineral  constituents  of  the  coal,  and  upon  ignition  both  of 
these  materials  lose  weight,  and  the  weight  of  the  ignited  residue 
from  these  materials  is  less  than  the  weight  of  the  materials  as  they 
occur  in  the  coal.  A  corrected  ash  which  only  partially  corrects 
cannot  be  regarded  as  very  satisfactory  and  in  reporting  a  proxi- 
mate analysis  the  common  method  of  reporting  the  "  ignited 
mineral  residue  "  as  the  ash  is  certainly  to  be  preferred  to  uncer- 
tain and  possibly  misleading  "  corrected  ash  "  reports. 

Fusibility  of  the  ash.  The  fusibility  of  the  coal  ash  is  depen- 
dent upon  the  chemical  composition  and  physical  condition  of 
the  minerals  present.  The  ash  from  most  coals  is  highly  silicious 
but  the  variation  in  the  nature  and  amounts  of  the  different  con- 
stituents is  so  great  that  no  typical  composition  can  be  given.  The 
following  analyses  of  ash  from  different  coals  taken  from  Groves 
and  Thorpe1  serve  to  illustrate  this  point: 


No.  1. 

No.  2. 

No.  3. 

No.  4. 

No.  5. 

No.  6. 

SiO2 

64  21 

45  13 

'31  30 

15.48 

3  12 

1  70 

A1203  
Fe2O3  
CaO  
MgO  
K2O  

28.78 
2.27 
1.34 
1.12 

2.28 

22.47 

25.83 
2.80 
0.52 
0.60 

8.31 
54.47 
3.44 
1.60 
0.07 

5.28 
74.04 
2.26 
0.26 
0.53 

29.50 
32.78 
20.56 
2.16 
0.99 

2.12 
60.79 
19.20 
5.03 
0.35 

Na2O  . 

0.28 

0.29 

1.72 

0.08 

CaSO4 

2  37 

0  52 

2  17 

9  17 

10  71 

Chemical  Technology. 


COMPOSITION  AND  HEATING   VALUE  5 

The  fusibility  of  the  ignited  and  well-mixed  ash  is  dependent 
Upon  the  ratio  of  the  silica  to  the  bases  present,  upon  the  parties 
lar  bases  and  upon  the  percentage  of  alumina  present.  Mixtures, 
extremely  high  in  silica,  or  extremely  high  in  bases  are  not  readily 
fusible.  As  a  rule  the  most  readily  fusible  mixtures  are  those  ap- 
proximating a  uni-silicate,  but  many  silicates  up  to  the  bi-silicate 
or  even  tri-silicate  composition  are  fusible  at  temperatures  be- 
tween 1000  and  1200°  C.  (1800  to  2200°  F.). 

According  to  Hofman1,  the  temperature  of  formation  of  some 
pure  ferrous  silicates  are  as  follows: 

4FeO,  SiO2   =82.8%    FeO,     17.2%    SiO2  =  1280°  C. 

3FeO,  2SiO2  =  64.3%    FeO,     35.7%    SiO2  =  1140°  C. 

FeO,  Si02   =54.55%  FeO,     45.45%  Si02  =  1110°  C. 

The  fusion  temperature  after  the  silicate  is  once  formed  is 
considerably  lower  than  the  temperature  of  formation. 

Replacing  a  portion  of  the  ferrous  oxide  by  calcium  oxide, 
magnesium  oxide,  potassium  oxide,  etc.,  gives  compounds  having 
a-  lower  formation  temperature  than  the  pure  ferrous  silicates. 
Replacing  a  part  of  the  silica  by  alumina  gives  compounds 
having  a  somewhat  higher  temperature  of  formation.  Ash  which 
is  low  in  iron  is  usually  so  highly  silicious  that  it  is  not  readily 
fusible.  Ash  from  coals  high  in  pyrite  is  necessarily  high  in  iron 
and  the  ratio  between  the  bases  and  silica  is  often  such  that  easily 
f-usible  compounds  may  be  formed. 

The  values  given  for  the  temperature  of  formation  of  the 
ferrous  silicates  are  of  interest  as  showing  the  possible  fusibility 
of  the  ash,  but  fusibility  of  well-mixed  ignited  ash  and  fusibility 
of  the  ash  in  the  coal  during  combustion  of  the  coal  are  two 
entirely  different  things.  The  first  is  dependent  upon  the  constitu- 
tion of  the  ash  as  a  whole;  the  second  is  dependent  upon  the 
nature  and  distribution  of  the  different  minerals  in  the  coal  acting 
separately  or  only  partially  mixed.  An  ash  may  form  clinker 
during  burning  of  the  coal  on  account  of  the  fusibility  of  a  portion 
of  the  mineral  matter  when  the  chemical  composition  of  the  ash 
taken  as  a  whole  indicates  that  clinker  should  not  form.  Also 
some  ashes  may  not  clinker  during  burning  of  the  coal  when  the 
chemical  composition  indicates  them  to  be  more  fusible  than 
other  ashes  which  do  clinker. 

1  Trans.  A.I.M.E.,  Vol.  29. 


6  COAL 

In  the  coal  the  different  minerals  constituting  the  ash  do  not 
always  occur  mixed  intimately,  but  lumps  of  minerals  of  different 
composition  may  be  scattered  irregularly  through  the  coal.  Some 
of  these  lumps  in  themselves  may  be  fusible  or  form  fusible  com- 
pounds during  the  burning  of  the  coal.  The  effect  of  lumps  of 
pyrite  on  the  clinkering  of  coal  is  discussed  under  "  Sulphur." 

On  account  of  this  irregular  distribution  of  mineral  constitu- 
ents in  the  coal  any  effort  to  establish  a  close  relation  of  the  clinker- 
ing  properties  of  the  coal  ash  and  the  composition  of  the  entire 
ash  will  always  be  more  or  less  unsatisfactory  and  uncertain. 
The  composition  of  the  ash  as  a  whole  tells  nothing  at  all  as  to  the 
regularity  or  irregularity  of  distribution  of  the  different  mineral 
constituents  in  the  coal. 

Amount  of  ash  in  coal.  The  quantity  of  ash  is  so  variable 
that  no  definite  statement  as  to  the  percentage  can  be  given. 
Clean  lumps  of  some  coals  occasionally  contain  as  low  as  1  per  cent 
of  ash  while  dirty  slack  may  contain  as  high  as  25  per  cent.  Selected 
lumps  of  coal  from  Ohio  seams  may  be  as  low  as  2  per  cent  in  ash, 
but  no  mine  can  average  that  figure  on  its  actual  output.  The 
best  shipments  are  nearer  6  per  cent  in  ash  while  much  of  it  may 
be  9  to  10  per  cent.  In  shipments  of  slack,  the  ash  may  be  as 
high  as  14  or  15  per  cent  or  even  more.  The  same  statement  as 
to  specimen  analyses  which  was  given  under  "  moisture  "  is  also 
applicable  in  regard  to  ash,  namely,  that  the  content  of  ash  in 
picked  lumps  or  clean  coal  is  likely  to  be  much  lower  than  the 
average  ash  content  of  the  shipment  received  by  the  consumer. 

SULPHUR 

Forms  in  which  it  occurs.  One  of  the  most  prominent  forms 
in  which  it  occurs  is  iron  pyrite  (FeS2) .  In  some  cases  the  pyrite 
is  scattered  in  large  masses  or  in  partings  and  is  readily  recognized 
as  such.  In  other  cases  it  occurs  in  a  very  finely  divided  form,  the 
separate  particles  being  too  small  to  be  readily  recognized.  An- 
other important  form  in  which  sulphur  occurs  is  what  is  known 
as  organic  sulphur,  or  sulphur  combined  with  carbon  or  carbon 
and  hydrogen.  Some  Ohio  coals  show  as  much  as  2  per  cent  of 
organic  sulphur.  Occasionally  sulphur  occurs  in  coal  in  the  form 
of  free  sulphur  but  the  amount  of  such  is  usually  quite  small.  In 
weathered  coal,  such  as  coal  near  the  outcrop  of  the  seam,  or  the 


COMPOSITION  AND  HEATING   VALUE  7 

coal  in  the  face  of  an  old  entry  or  room,  or  in  piles  of  slack  which 
have  been  standing  for  some  time  exposed  to  air  and  moisture, 
some  of  the  sulphur  is  present  as  sulphate  of  iron,  lime  and  alumina, 
some  forms  of  pyrite  oxidizing  very  readily  upon  exposure  to  air. 

Heating  value  of  sulphur.  The  unoxidized  form  of  sulphur  on 
combustion  of  the  coal  is  burned  to  sulphur  dioxide,  which  burning 
is  accompanied  by  the  liberation  of  heat.  Where  it  occurs  as 
ferrous  sulphate  or  calcium  sulphate  it  has  no  heating  value  and 
during  the  combustion  of  the  coal  the  decomposition  of  these 
sulphates  absorbs  heat.  The  amount  of  oxidized  sulphur  in 
unweathered  coal  is,  however,  too  small  to  be  of  practical  import- 
ance and  for  freshly  mined  coal  sulphur  may  be  credited  with  a 
heating  value  of  from  approximately  2250  to  2950  calories  (4050 
to  5300  British  thermal  units),  the  different  values  depending 
upon  whether  it  is  present  as  organic  sulphur  or  as  pyrite 
(FeS2).  If  present  as  pyrite,  the  heat  of  its  combustion  which 
results  in  the  formation  of  sulphur  dioxide  (862)  and  ferric  oxide 
(Fe2O3)  is  approximately  700  calories  (1250  British  thermal 
units)  higher  than  the  combustion  of  sulphur  in  organic  form 
to  sulphur  dioxide. 

Sulphur  in  weathered  coal.  In  weathered  coal  the 
presence  of  sulphates  may  very  decidedly  affect  the  heating  value 
per  unit  of  coal,  as  may  be  shown  by  the  following:  One  per  cent 
of  sulphur  as  pyrite  in  coal  has  a  heating  value  of  about  29| 
calories.  During  combustion  of  the  coal  the  decomposition  of  the 
ferrous  sulphate  (FeSO4  TH^O)  corresponding  to  1  per  cent  of 
sulphur  absorbs  about  21 J  calories  of  heat,  which  is  a  net  loss  in 
heating  value  of  about  51  calories  or  about  three-fourths  of  one 
per  cent  of  the  heating  value  of  the  coal.  If  this  were  the  only 
effect  it  would  not  be  so  important  as  the  amount  of  sulphur 
present  as  sulphate  does  not  often  exceed  1  per  cent.  However, 
1  per  cent  of  sulphur  as  pyrite,  on  oxidation,  absorbs  2  per  cent  by 
weight  of  oxygen  and  absorbs  and  combines  with  about  4  per  cent 
of  water  which  is  not  given  up  on  air  drying  so  that  the  appar- 
ently air  dry  coal  may  be  6  per  cent  heavier  on  account  of  this 
oxidation  of  1  per  cent  of  sulphur,  and  the  calorific  value  per  unit 
of  coal  instead  of  being  only  three-fourths  per  cent  lower,  may  be 
actually  nearly  7  per  cent  lower  in  heating  value. 

Action  of  sulphur  dioxide.  Upon  the  cooling  of  the  flue  gases 
the  sulphur  dioxide  formed  during  the  combustion  of  the  coal 


8  COAL 

unites  with  water  and  forms  sulphurous  acid,  which  as  such 
or  upon  further  oxidation  to  sulphuric  acid  has  a  corrosive 
effect  upon  metallic  structures.  This  corrosive  action  takes  place 
after  cooling  and  the  popular  idea  that  sulphur  in  coal  causes  cor- 
rosion of  boiler  tubes,  etc.,  by  action  of  sulphur  dioxide  is  largely 
without  real  foundation. 

Relation  of  sulphur  to  clinkering  of  the  ash.  When  the  sul- 
phur occurs  in  the  coal  as  pyrite,  as  it  usually  does,  it  is  objection- 
able for  two  reasons : 

First,  the  oxide  of  iron  produced  during  combustion  may  unite 
with  other  constituents  of  the  ash  and  produce  a  fusible  compound 
or  clinker.  Oxide  of  iron  by  itself  produces  no  clinker,  but  as  has 
been  stated  under  "  ash,"  the  other  mineral  constituents  of  the 
coal  are  usually  highly  silicious  and  oxide  of  iron  in  contact  with 
silica  or  silicates  at  a  high  temperature  is  very  liable  to  result 
in  the  production  of  easily  fusible  silicates  (or  clinkers).  The 
higher  the  temperature  the  more  readily  this  fusion  occurs  and  the 
operation  of -a  furnace  so  as  to  keep  the  grate  bars  and  the  lower 
portion  of  the  fuel  bed  at  a  relatively  low  temperature  may  result 
in  a  clean  ash,  when  the  same  coal  with  hot  grate  bars  and  a  hot 
bed  of  ash  may  clinker  badly. 

Second,  pyrite  (FeS2)  on  being  heated  gives  off  approximately 
one-half  of  its  sulphur,  and  a  compound  approximating  the  formula 
(FeS)  remains.  This  ferrous  sulphide  is  fusible  at  a  red  heat  and 
in  the  combustion  of  coals  containing  pyrite  in  pieces  of  consider- 
able size,  lumps  of  this  ferrous  sulphide  may  fuse  before  they  have 
had  an  opportunity  to  burn,  and  may  be  starting  points  for  the 
formation  of  a  clinker  which  may  render  it  difficult  to  satisfactorily 
burn  the  coal.  Finely  disseminated  pyrite  will  not  produce  this 
kind  of  trouble,  but  finely  disseminated  pyrite  and  a  uniform  dis- 
tribution of  highly  silicious  ash  is  a  condition  very  favorable  for 
the  formation  of  clinker.  Organic  sulphur  has  no  tendency  to 
form  clinker,  hence  high  sulphur  in  coal  is  by  itself  not  a  certain 
index  of  the  clinkering  qualities  of  the  ash.  As  a  general  rule,  the 
higher  the  sulphur  the  greater  the  probability  that  the  ash  will 
clinker,  but  with  frequent  exceptions  due  to  the  presence  of  the 
sulphur  in  an  organic  form  or  due  to  the  fact  that  the  other  mineral 
constituents  of  the  coal  are  not  present  in  forms  or  quantities 
favorable  to  the  production  of  clinker. 


COMPOSITION  AND  HEATING   VALUE 


TOTAL  HEATING   VALUE   OF   COAL 

This  is  the  total  number  of  calories  or  British  thermal  units 
developed  when  a  unit  weight  of  the  coal  is  burned.  Expressed  in 
a  general  way,  it  is  the  number  of  unit  quantities  of  water  which 
are  raised  one  degree  by  the  total  heat  from  the  combustion  of  a 
unit  weight  of  coal.  Expressed  in  calories  it  is  the  number  of  grams 
of  water  which  can  be  raised  one  degree  Centigrade  by  the  heat 
from  the  combustion  of  one  gram  of  coal.  Expressed  in  British 
thermal  units,  it  is  the  number  of  pounds  of  water  which  can  be 
raised  one  degree  Fahrenheit  by  the  heat  from  the  combustion  of 
one  pound  of  coal. 

The  specific  heat  of  water  is  not  uniform  at  different  tempera- 
tures and  an  exact  definition  requires  the  defining  of  the  particular 
temperature  through  which  the  water  is  raised.  The  temperature 
most  usually  taken  is  from  15  to  16°  C.  or  62  to  63°  F.  With  this 
restriction  the  definition  of  the  calorific  value  of  a  coal  is  the 
number  of  grams  of  water  which  can  be  raised  from  15  to  16°  C. 
by  the  heat  from  the  combustion  of  one  gram  of  coal. 

Relation  of  British  thermal  value  to  calorific  value.  In  any 
given  coal  the  relation  between  the  heating  value  in  calories  and  in 
British  thermal  units  is  as  follows : 

Let  the  calorific  value  =  a,  and 
the  B.t.u.  value    =6. 

then  the  combustion  of  1  gram  of  coal  raises  a  grams  of  water 
1°  C.  and  the  combustion  of  one  pound  of  coal  raises  6  pounds 
of  water  1°  F.  Evidently  as  far  as  amounts  of  coal  and  water  arc 
concerned  a  and  b  will  be  numerically  equal  and  the  only  thing 
in  the  two  expressions  which  will  cause  them  to  be  unequal  is 
the  difference  in  the  unit  of  temperature. 

1°  C.  =  |°  F.  or  1°  F.  =  J°  C. 

In  expressing  the  value  in  British  thermal  units  the  unit  of 
water  is  raised  only  |  as  far  as  it  is  in  expressing  the  value  in  calor- 
ies, hence  1  as  many  units  can  be  raised,  or  numerically, 

b  =  5  a  and  conversely  a  =  I  b. 


10  COAL 

or  in  general, 

The  heating  value  in  B.t.u.  =  f  the  heating  value  in  calories. 
The  heating  value  in  calories  =  f  the  heating  value  in  B.t.u. 

If  it  is  desired  to  express  the  amount  of  heat  in  a  given  weight 
of  coal  in  British  thermal  units  and  in  calories  the  relation  between 
one  pound  and  one  gram  must  be  considered.  One  pound  avoir- 
dupois=  453.6  grams.  Since  a  British  thermal  unit  is  the  heat 
necessary  to  raise  one  pound  of  water  one  degree  Fahrenheit,  to 
express  this  value  in  calories  the  equivalent  in  grams  and  degrees 
Centigrade  must  be  substituted,  or  one  B.t.u.  =453.  6  grams  of 
water  raised  I  of  one  degree  Centigrade,  from  which  1  B.t.u.  = 
252  small  calories.  Expressing  calories  in  B.t.u.,  one  small  calorie 

.t.u.  =  0.003967  B.t.u. 


Heat  producing  constituents  of  coal.  The  heat  of  combus- 
tion of  coal  is  due  essentially  to  the  heat  produced  by*the  oxida- 
tion of  the  carbon  plus  the  heat  produced  by  the  oxidation  of  the 
hydrogen  not  combined  with  oxygen  plus  the  oxidation  of 
unoxidized  forms  of  sulphur  and  iron.  The  amount  of  heat  pro- 
duced by  the  combustion  of  these  elements  in  combination  is  not 
always  exactly  the  same  as  that  produced  by  the  combustion  of 
the  free  elements  separately.  However,  the  difference  is  not  so 
great  but  that  the  heat  can  be  calculated  with  a  fair  degree  of 
accuracy  from  the  amounts  of  these  elements  present. 

Calculation  of  heating  value  from  chemical  composition. 
Many  different  formulas  have  been  and  are  used  in  calculating 
the  heating  value  from  the  chemical  analysis.  One  of  the  best 
known  and  most  generally  used  is  Dulong's  formula,  which  is 
commonly  stated  as  follows: 

The  heating  value  =  (8080  X  the  carbon)  +  [34460  X  (the  hydro- 
gen— i  the  oxygen)  ]+  (2250  X  the  sulphur).  The  results  for  heat- 
ing values  obtained  by  the  use  of  this  formula  are  usually  within 
less  than  1  1  per  cent  of  the  actual  value  as  determined  in  the  calo- 
rimeter. About  150  analyses  of  Ohio  coals  given  in  Bulletin  No.  9 
of  the  Ohio  Geological  Survey,  show  that  the  values  by  Dulong's 
formula  range  from  about  30  to  about  100  calories  lower  than  the 
value  as  determined  in  the  calorimeter.  Inspection  of  the  deter- 
mined and  calculated  values  of  the  coals  given  in  Chapter  X0 


COMPOSITION  AND  HEATING   VALUE  11 

shows  a  very  fair  agreement  between  the  calculated  and  determined 
values. 

High  oxygen  coals  show  a  calculated  value  considerably  lower 
than  the  determined  value,  and  the  calculated  values,  as  a  whole, 
are  lower  than  the  determined  values.  Two  factors  may  help  to 
account  for  the  greater  part  of  this  difference:  (1)  The  latest  value 
given  for  the  heat  of  combustion  of  carbon  is  about  8100  instead 
of  8080  as  used  in  Dulong's  formula.  If  this  higher  value  for  car- 
bon be  used,  the  calculated  calorific  values  will  be  raised  from  10 
to  15  calories  on  each  sample.  (2)  The  determined  calorific  values 
given  were  in  all  cases  based  upon  the  heating  value  of  naphthalene 
as  9692.  Later  values  by  Atwater,  Fischer  and  Wrede  and  the 
U.  S.  Bureau  of  Standards  are  considerably  lower  than  this.  If 
the  value  for  naphthalene  be  taken  as  low  as  9628 — Atwater's 
value —  this  will  lower  the  determined  calorific  values  given  by 
about  50  calories.  The  effect  of  these  two  causes  if  applied  to  the 
values  given  brings  the  calculated  and  determined  values  much 
nearer  together  with  the  calculated  value  still  somewhat  lower 
than  the  determined  value. 

Some  of  the  differences  between  the  calculated  and  determined 
values  are  very  probably  due  to  errors  in  the  determination,  while 
others  probably  correspond  to  actual  differences  in  the  heat 
developed  by  the  combustion  of  the  different  elements  in  the  com- 
binations in  which  they  exist  in  the  coal.  Some  organic  compounds, 
such  as  carbon  bisulphide,  have  a  decidedly  higher  calorific  value 
than  the  calorific  value  of  equivalent  amounts  of  the  elements 
present.  In  other  words,  the  decomposition  of  the  carbon  bisul- 
phide into  its  elements  liberates  heat.  Such  compounds  are  known 
as  endothermic  compounds.  The  low  results  obtained  by  Dulong's 
formula  on  some  coals  indicate  the  presence  of  endothermic 
compounds  in  the  coal. 

Distribution  of  oxygen  in  coal  and  modification  of  Dulong's 
formula.  A  small  portion  of  the  oxygen  (in  some  high  volatile 
and  high  moisture  coals,  a  considerable  portion)  is  present  in  coal 
in  combination  with  the  carbon  or  at  least  it  escapes  in  com- 
bination with  the  carbon  as  carbon  dioxide  (CO2)  and  as  carbon 
monoxide  (CO)  instead  of  in  combination  with  the  hydrogen  as 
water  (H^O),  when  the  coal  is  decomposed  and  the  volatile 
matter  is  given  off.  Hence  Dulong's  formula  should  be  con- 
sidered merely  as  a  means  of  estimating  heating  value  rather 


12  COAL 

than  that  the  composition  of  the  coal  is  in  exact  agreement  with 
the  formula.  Any  oxygen  combined  with  carbon  has  a  smaller 
effect  in  reducing  the  heating  value  than  if  it  is  combined  with 
hydrogen,  and  some  calculated  heating  values  agree  more  closely 
with  the  determined  ones  on  the  assumption  that  carbon  and 
oxygen  are  combined  rather  than  the  oxygen  and  the  hydrogen. 
On  this  assumption,  Dulong's  formula  would  be  modified  to  read 
as  follows: 

(C-fO)  8080+H(34460)  +8(2250). 

In  certain  compounds  the  estimation  of  the  heating  value  by 
this  formula  is  closer  to  the  determined  value  than  the  estimation 
by  Dulong's  formula  unmodified.  For  example,  cane  sugar 
(Ci2H220n)  contains  42.1  per  cent  carbon;  6.43  hydrogen  and 
51.47  oxygen. 

The  determined  calorific  value  of  cane  sugar  is  3958  calories. 
The  calculation  of  the  heating  value  by  Dulong's  formula  is  3402 
calories.  By  the  modified  formula,  assuming  the  oxygen  with  the 
carbon  =  4058  calories.  Neither  calculated  value  agrees  with  the 
determined  value.  The  value  calculated  by  Dulong's  formula  is 
556  calories  too  low  and  the  value  calculated  by  the  modification  is 
200  calories  too  high.  For  this  particular  material  a  composite 
formula,  assigning  a  portion  of  the  oxygen  to  the  carbon  and  a 
portion  to  the  hydrogen,  is  necessary  to  obtain  a  calculated  result 
in  agreement  with  the  determined  value.  Many  high  oxygen 
coals  give  better  calculated  values  with  a  slightly  modified  formula 
instead  of  the  regular  Dulong  formula.  However,  each  class 
of  coal  requires  a  particular  modification  and  often  the  ultimate 
analyses  themselves  may  be  inaccurate  so  that  special  modifica- 
tions to  fit  particular  samples  are  to  be  accepted  with  caution. 

Heat  calculation  formulas  and  actual  chemical  composition. 
The  actual  heating  value  of  a  fuel  is  the  final  heat  evolved  by 
complete  combustion  and  may  be  and  usually  is  the  net  result 
of  a  number  of  intermediate  reactions.  In  such  a  complex  sub- 
stance as  coal  little  is  known  as  to  the  exact  nature  of  the  material 
and  of  these  intermediate  reactions  and  the  agreement  or  non- 
agreement  of  the  actual  and  calculated  heating  values  proves 
nothing  as  to  the  exact  chemical  composition.  On  account  of 
this  lack  of  knowledge  as  to  exactness  of  composition  and  as  to 
the  nature  of  the  intermediate  decomposition  reactions  it  is  not 


COMPOSITION  AND  HEATING   VALUE  13 

possible  to  give  an  exact  general  formula  for  the  heating  value 
of  coal  based  on  its  chemical  composition  and  any  and  all  formulas 
must  be  regarded  merely  as  more  or  less  exact  approximations. 
These  approximations  are  in  general  of  practical  value  only  in 
so  far  as  they  accord  with  actual  determinations.  However, 
to  the  chemist  the  calculated  calorific  value  has  a  special  appli- 
cation in  that  it  serves  as  a  check  on  the  laboratory  work.  For 
any  given  set  of  samples  of  the  same  kind  of  coal  with  accurate 
calorimeter  and  ultimate  determinations,  the  agreement  or  dis- 
agreement between  the  calculated  and  the  determined  calorific 
values  should  show  considerable  uniformity  and  any  considerable 
error  in  a  particular  calorimeter  or  ultimate  determination  will 
usually  be  discovered  upon  comparing  the  calculated  and  deter- 
mined calorific  values. 

In  the  past  much  importance  and  stress  have  been  placed  on 
calculated  values  but  at  present  bomb  calorimeters  are  in  such 
general  use  that  calculated  values  are  apt  to  be  more  of  special 
interest  to  the  chemist  than  of  practical  importance  to  the  con- 
sumer and  discussions  as  to  just  what  formulas  are  the  most 
applicable  are  of  no  great  practical  interest  to  the  average  coal 
user  or  producer. 

PRACTICALLY   AVAILABLE    HEATING    VALUE    OF   A    COAL 

This  is  the  amount  that  can  be  utilized,  or  is  the  total  heating 
value  less  the  losses  necessary  or  incident  to  combustion.  For  a 
steam  boiler,  the  losses  are  as  follows: 

(1)  The  latent  heat  in  evaporating  the  water  in  the  coal,  in- 
cluding moisture,  combined  water  and  water  formed  during  com- 
bustion. 

'  (2)  The  heat  carried  up  the  stack  as  sensible  heat  by  the  prod- 
ucts of  combustion. 

(3)  The  heat  carried  up  the  stack  by  the  excess  air  used  in 
burning  the  coal. 

(4)  The  heat  lost  by  incomplete  combustion,  as  formation  of 
carbon  monoxide  (CO)  instead  of  carbon  dioxide  (CO2). 

(5)  Heat  not  realized  from  the  unburned  coal  in  the  ash  pit. 
(7)  Radiation  and  other  losses. 

The  relative  amounts  of  these  losses  expressed  in  percentages 
range  about  as  follows:  Latent  heat,  3  to  5  per  cent;  sensible 


14  COAL 

heat,  8  to  14  per  cent;  excess  air,  8  to  25  per  cent;  carbon 
monoxide  (CO),  0  to  5  per  cent;  unburned  coal,  1  to  10  per  cent; 
radiation  and  other  losses,  3  to  15  per  cent.  The  sum  of  all  the 
losses  is  usually  between  25  and  50  per  cent,  leaving  an  available 
value  of  50  to  75  per  cent.  The  actually  available  value  varies 
with  the  kind  of  coal,  the  type  of  stoker  and  boiler  used  and  the 
completeness  of  the  combustion.  The  best  boiler  tests  give  an 
available  heating  value  for  the  best  coals  as  high  as  75  per  cent, 
while  poor  practice  and  inferior  coals  may  give  an  available  heat- 
ing value  as  low  as  50  per  cent.  Losses  Nos.  2,  3,  4,  5  and  7  are, 
within  limits,  under  control  of  the  boiler  crew  and  up  to  15  per 
cent  of  the  total  heat  may  be  saved  or  lost  depending  upon  how 
the  fire  is  operated.  This  means  as  high  as  20  per  cent  of  the 
available  value  and  when  fuel  bills  amount  to  thousands  of 
dollars,  an  increase  in  efficiency  by  having  at  least  an  occasional 
expert  inspection  and  test  run  ought  to  be  money  well  spent. 

When  two  plants  operating  on  practically  the  same  equipment 
and  using  the  same  grade  of  coal  vary  greatly  in  the  efficiency  ob- 
tained one  or  both  of  the  plants  need  inspection.  Equipment  for 
flue-temperature  measurements  and  adequate  apparatus  for  mak- 
ing flue-gas  analyses  are  usually  profitable  investments.  The 
determinations  which  should  be  made  on  the  flue  gases  are  the  de- 
termination of  the  amounts  of  carbon  dioxide  (CO2),  oxygen  (62) 
and  carbon  monoxide  (CO)  present.  The  determination  of  carbon 
dioxide  alone  by  mechanical  devices  or  other  means  may  give 
fairly  satisfactory  control  if  checked  by  properly  taken  Orsat 
determinations.  Mechanical  or  automatic  devices  left  to  take 
care  of  themselves  may  be  worse  than  useless.  For  details  and 
discussion  of  flue  gas  sampling  and  analysis,  see  Chapter  XL 

DETERMINATION   OF  THE  HEAT  LOSSES; 

An  illustration  of  the  values  and  methods  of  obtaining  these 
losses  is  as  follows: 

(1)  Latent  heat. — The  amount  of  this  loss  is  dependent  upon 
the  coal  used  and  is  not  subject  to  control  by  the  firemen  operating 
the  furnace  unless  the  coal  is  wet  down  intentionally  by  the  fire- 
men, in  which  case  the  latent  heat  loss  is  greater  than  the  amount 
calculated  from  the  analysis.  The  amount  of  hydrogen  in  the  coal 
as  determined  by  analysis  multiplied  by  9  equals  the  amount 


COMPOSITION  AND  HEATING   VALUE  15 

of  water  present  in  the  coal  together  with  that  formed  during 
combustion.  This  amount  of  water  multiplied  by  539.1+0.52 
(100  —  f)  equals  the  calories  of  heat  lost.  Where  539 . 1  is  the  latent 
heat  in  evaporating  the  water  at  100°  C.;  t  is  the  boiler  room 
temperature  in  degrees  Centigrade  and  0.52  (100  —  0  equals  the 
difference  between  the  specific  heat  of  water  and  the  specific  heat 
of  water  vapor  for  the  range  100  —  t  degrees.  The  other  portion 
0.48  (100  —  t)  is  taken  care  of  under  sensible  heat  carried  off  by  the 
products  of  combustion  where  it  is  assumed  that  the  water  is 
evaporated  at  the  boiler  room  temperature  and  the  sensible  heat 
of  water  vapor  calculated  from  that  temperature.  The  above 
value  for  latent  heat  of  water  at  212°  F.  is  that  given  by  Marks 
and  Davis1  and  is  based  upon  the  work  of  Joly  and  Henning.  The 
above  formula  for  British  thermal  units  is, 

B.t.u.  =970. 4+0. 52(212-0, 

with  £  =  boiler  room  temperature  in  degrees  Fahrenheit. 

(2)  Products  of  combustion.  The  products  of  complete  combus- 
tion are  carbon  dioxide,  water  vapor,  sulphur  dioxide,  nitrogen 
and  ash.  The  amounts  of  these  obtained  from  the  unit  weight  of 
coal  are  3f  times  the  carbon  for  the  carbon  dioxide;  nine  times  the 
hydrogen  for  the  water  vapor;  two  times  the  sulphur  for  the  sul- 
phur dioxide,  and  the  ash  and  nitrogen  as  shown  by  the  analysis. 
The  water  equivalent  of  the  products  of  combustion  is  obtained 
by  multiplying  each  of  these  items  by  its  specific  heat  and  adding 
the  products. 

The  weight  of  the  nitrogen  in  the  air  used  for  combustion  is 
equal  to  very  nearly  3.33  times  the  weight  of  the  oxygen  required 
for  combustion.  This  oxygen  is  equal  to  2f  times  the  carbon,  plus 
eight  times  the  hydrogen,  plus  the  sulphur  minus  the  oxygen  con- 
tained in  the  coal.  The  nitrogen  thus  obtained  multiplied  by  the 
specific  heat  of  nitrogen  gives  the  water  equivalent  of  the  nitro- 
gen from  the  air.  Similarly  the  amount  of  ash  multiplied  by  its 
specific  heat  gives  the  water  equivalent  of  this  item. 

The  sum  of  all  the  water  equivalents  obtained  as  above  mul- 
tiplied by  the  difference  between  the  temperature  at  which  the 
products  escape  and  the  temperature  of  the  air  supplied  for  com- 

1  Tables  and  Diagrams  of  Thermal  Properties  of  Saturated  and  Super- 
saturated Steam. 


16  COAL 

bustion  gives  the  heat  carried  off  in  the'  products  of  combus- 
tion. 

(3)  Excess  air.  The  excess  air  present  is  equal  to  the  amount 
of  air  required  for  combustion  multiplied  by  the  ratio  of  the 
excess  air  to  that  required.  The  weight  of  air  required  for 
combustion  is  4.33  times  the  oxygen  required  for  combustion, 
or  4.33  times  the  sum  of  I  of  the  carbon,  plus  8  times  the  hydro- 
gen plus  the  sulphur  minus  the  oxygen  in  the  coal.  The  ratio 
of  the  excess  air  present  to  that  used  for  combustion  is  obtained 
from  the  analysis  of  the  gases  passing  out  of  the  chimney.  If 
the  small  amount  of  nitrogen  present  in  coal  be  neglected  the 
ratio  of  the  air  present  in  the  chimney  gases  to  the  air  used  in 
combustion  is  equal  to 

Oxygen 

0.3  Nitrogen— Oxygen' 

in  which  the  oxygen  and  nitrogen  are  percentages  by  weight  of 
the  gases.  Where  the  percentages  are  given  by  volume  the  for- 
mula becomes: 

Oxygen 


Nitrogen     „ 
--  -Oxygen 


Calculation  of  the  excess  air.     The  derivation  of  the  above 
formula  for  excess  air  is  as  follows: 

,~         ,  .       „  ,,  .  the  excess  air 

The  ratio  of  the  excess  air 


the  air  required  for  combustion 

In  the  flue  gas  the  oxygen  present  is  that  which  is  in  the  excess 
air.  The  nitrogen  present  is  the  nitrogen  from  the  air  required 
plus  the  nitrogen  in  the  excess  air.  The  required  air  equals  the 
total  air  minus  the  excess  air.  By  volume,  air  is  composed  of 
20.8  parts  oxygen  and  79.2  parts  nitrogen  or  for  every  4.8  parts 
of  air  there  are  3.8  parts  of  nitrogen  and  one  part  of  oxygen. 
The  excess  air  is  found  from  the  amount  of  oxygen  present  and  is 
equal  to  4.8  times  the  oxygen  present.  The  total  air  is  determined 

•1    Q 

from  the  total  nitrogen  present  and  is  equal  to  ^  ^  times  the  total 

o.o 

nitrogen.    Subtracting  the  excess  air  (4.8  times  the  oxygen)  from 


COMPOSITION  AND  HEATING  VALUE  17 

the  total  air  ( -  5  times  the  nitrogen )  gives  the  air  required  for 
\d.o  / 


combustion  as 


-  nitrogen— 4.8  oxygen, 
o.o 


Substituting  these  values  for  the  excess  air  and  the  required  air, 
the  ratio  of  the  excess  air  equals 

4.8  Oxygen 


4  8 

^-r  Nitrogen  —  4.8  Qxygen 

o.o 

and  dividing  by  4.8  gives  the  formula  in  the  form  as  given  above: 

Oxygen 

Nitrogen 

T—Q-f Oxygen 

o.o 

The  formula  by  weight  is  obtained  in  a  similar  manner. 

As  an  illustration,  when  the  flue  gas  by  volume  analyzes  as 
follows : 

CO2 9. 2  per  cent 

O2 10.9  per  cent 

CO 0.0  per  cent 

N2 79 . 9  per  cent 


Total 100.0  per  cent 

the   excess  air,  by  substituting  these  values  in  the  formula,  is 

^°^   =1.08 


or  108  per  cent  of  the  air  required  for  combustion. 

These  formulas  are  applicable  only  where  the  amount  of 
nitrogen  in  the  fuel  is  so  small  as  to  be  neglected  as  in  the  case 
of  coals.  If,  however,  the  fuel  contains  nitrogen  in  considerable 
quantity,  which  is  the  case  with  some  gaseous  fuels,  the  formula 


18 


COAL 


is  modified  to  allow  for  the  nitrogen  present  in  the  fuel.     The 
formula  where  the  percentages  are  given   by  volume  becomes 


Oxygen 


Nitrogen 


V'E 


3.8 


—  Oxygen 


where  V  is  the  volume  of  gaseous  carbon  in  100  volumes  of  flue 
gas  and  V  the  volume  of  gaseous  carbon  in  100  volumes  of  fuel 
gas  and  E  is  the  percentage  by  volume  of  nitrogen  in  the  fuel  gas. 
The  derivation,  of  this  modified  formula  is  as  follows:  For 
convenience  in  calculation,  the  molecule  of  carbon  in  a  gaseous 
state  is  usually  considered  as  composed  of  two  atoms.  As  all 
the  carbon  in  the  fuel  is  present  in  the  products  of  combustion 
the  relation  of  the  volume  of  the  fuel  gas  to  the  volume  of  the 
flue  gas  is  obtained  by  comparison  of  the  ratio  of  the  volumes 
of  the  carbon  present  in  the  two  gases,  from  which  the  volume 
of  nitrogen  in  the  fuel  gas  can  be  determined  in  terms  of  the 
volume  of  the  flue  gas.  This  is 

V'E 
V 

The  nitrogen  in  the  total  air  required  for  combustion  is  accord- 
ingly the  total  nitrogen  in  the  flue  gas  minus  the  nitrogen  in  the 
fuel  gas  or 

V'E 
Nitrogen =-. 

To  make  this  clearer  by  a  special  example,  suppose  the  fuel 
gas  and  the  flue  gas  by  volume  to  have  the  following  composition: 


Fuel  Gas. 

Flue  Gas. 

Carbon  dioxide  (CO2)                                •    •  • 

4  5 

14  5 

Oxygen  (O2)  
Ethylene  (C2H4) 

0.5 
1  0 

2.9 

Carbon  monoxide  (CO)        .                 .  . 

22  0 

Hydrogen  (H2)  

9.5 

Methane  (CH4) 

3  5 

Nitrogen  (N2)      .                               

59.0 

82  6 

100.0 

100.0 

COMPOSITION  AND  HEATING   VALUE  19 

The  volume  of  carbon  molecules  in  the  fuel  gas  is  as  follows: 

iXCO2  =  2.25 
1XC2H4  =  1.00 
iXCO  =11.00 
iXCH4  =  1.75 


Total  =16.00 

In  the  flue  gas  the  volume  of  the  carbon  molecules  equals  J  the 
C02  =  7.25.     Substituting  these  values  in  the  formula,  it  becomes: 


(59) 


16       -2.9 


3.8 

or  24  per  cent  of  the  air  required  for  combustion. 

These  calculations  may  be  made  if  desired  on  the  assumption 
of  one  atom  in  the  gaseous  carbon  molecule  in  which  case  the 
volume  of  the  carbon  molecules  in  each  gas  will  be  twice  as  great, 
but  they  will  have  the  same  ratio  to  each  other  and  the  same 
numerical  result  is  obtained. 

(4)  Incomplete  combustion.  The  heat  lost  by  incomplete 
combustion  or  formation  of  CO  instead  of  CO2  is  determined 
as  follows:  One  gram  of  carbon  burned  to  002  =  8080  calories. 
One  gram  of  carbon  burned  to 'CO  =  2430  calories,  or  the  heat 
loss  due  to  the  formation  of  CO  instead  of  CO2  is  8080  —  2430 
=  5650  calories.  The  amount  of  carbon  which  is  burned  to  CO 
instead  of  C02  is  determined  from  the  flue  gas  analysis  and  the 
amount  of  carbon  present  in  a  unit  of  coal.  Since  equal  volumes 
of  CO  and  CO2  contain  equal  amounts  of  carbon,  the  ratio  of 
carbon  burned  to  CO  instead  of  CO2  is  equal  to  the 

CO  by  volume 


C02  by  volume + CO  by  volume' 

Multiplying  the  percentage  of  carbon  present  in  the  coal  by  this 
ratio  gives  the  actual  amount  of  carbon  burned  to  CO  per  unit 
of  coal  fired.  This  multiplied  by  5650,  equals  the  calories  of 
heat  lost. 


20  COAL 

(5)  Unburned  coal.  The  heat  not  realized  from  unburned 
coal  in  the  ash  pit  is  also  a  large  loss  in  many  cases.  The  total 
calories  of  heat  lost  is  the  amount  of  unburned  coal  times  the 
calorific  value  of  the  coal. 

Calculation  of  amount  of  unburned  coal.  The  amount  of 
unburned  coal  is  determined  from  the  analysis  of  the  refuse  taken 
from  the  ash  pit  and  the  analysis  of  the  coal  as  fired. 

Let  the  ash  in  the  coal  by  analysis  =  a.  Then  the  total 
volatile  and  combustible  matter  including  moisture  and  fixed 
carbon  in  the  coal  by  analysis  =  1  —  a. 

Let  the  volatile  and  combustible  matter  or  ignition  loss  in 
the  refuse  —  c. 

Let  the  incombustible  matter  in  the  refuse  =  r,  all  of  these 
values  being  decimals. 

The  unburned  coal  in  the  refuse  expressed  in  terms  of  the 

refuse  =  —  — . 
1  — a 

The  ash  in  this  unburned  coal  in  the  refuse  expressed  in  terms 
of  the  refuse  is 

/  \ 

ca 


l-aj     1-ctj 

The  ash  in  the  unburned  coal  :  total  ash  :  :  the  unburned  coal  : 
total  coal.  Substituting  the  above  values,  this  proportion 
becomes : 

ca 

-  :  r::x  :  1, 
1  — a 

where  x  is  the  unburned  coal,  from  which 


As  a  particular  example  suppose  the  ash  in  the  coal=  10 
per  cent.  The  refuse  by  analysis  =  volatile  and  combustible 
30  per  cent,  incombustible  70  per  cent.  Substituting  these 
values, 

ca        0.3(0.10)     0.03 

(l-a)r     (0.9)  (0.7)     0.63 


COMPOSITION  AND  HEATING   VALUE  21 

In  which  case  the  loss  due  to  unhurried  coal  equals  the  calorific 
value  of  the  coal  times  0.049. 

(7)  Radiation.  The  radiation  and  other  losses.  The  sum 
of  1,  2,  3,  4  and  5  plus  the  heat  in  the  water  evaporated  sub- 
tracted from  the  total  calorific  value  of  the  coal  gives  the  radia- 
tion and  other  unaccounted  for  losses. 

Unaccounted  losses.  Some  of  the  unaccounted  losses  are 
as  follows: 

(a)  Traces  of  hydrogen  and  hydrocarbons  in  the  flue  gas. 

(6)  Unburned  carbon  in  soot  and  smoke. 

(c)  Latent  and  sensible  heat  due  to  water  used  to  wet  down 
the  coal  or  added  to  the  ash  pit. 

(d)  Sensible  heat  in  flue  gas  due  to  the  moisture  in  the  air. 
The  heat  losses  due  to  the  presence  of  traces  of  unburned 

hydrogen  or  methane  or  ethylene  in  the  flue  gas  are  usually  con- 
sidered as  small.  Certainly  no  large  amounts  of  these  gases 
are  found  in  the  escaping  flue  gas  but  the  presence  of  undeter- 
mined traces  of  any  of  these  gases  may  help  to  account  for  some 
of  the  unaccounted-for  losses.  As  an  example,  in  the  combus- 
tion of  No.  6  coal  with  100  per  cent  excess  air  and  a  flue-gas  analysis 
of  CO2,  9.3;  O2,  10.6;  CO,  0.0  and  N2  80.1  per  cent,  the  presence 
of  TOO  per  cent  of  hydrogen  (H2)  or  of  methane  (CH4)  or  of 
ethylene  (C2H4)  would  represent  a  heating  loss  approximately 
as  follows:  On  the  assumption  that  practically  all  of  the  0.66 
gram  of  carbon  in  one  gram  of  coal  fired  is  contained  in  the  9.3 
per  cent  of  CO2  in  the  flue  gas,  a  molecular  volume  22.4  liters 
of  CO2  =  44  grams  of  C02  =  12  grams  of  carbon.  A  molec- 
ular volume  of  hydrogen  =  2  grams  of  hydrogen,  from  which  1 
cubic  centimeter  of  hydrogen  contains  by  weight  one-sixth  as 
much  hydrogen  as  the  weight  of  the  carbon  in  1  cubic  centi- 
meter of  C02.  The  relative  volumes  of  hydrogen  and  CO2 
in  the  gas  on  the  assumption  of  j-J-j  per  cent  of  hydrogen  present 
is  as  1 :  930.  Hence  the  weight  jf  aydrogen  in  the  gas  correspond- 
ing to  1  gram  of  coal  tired  is  J -X  ^iuX  0.66  =  -g-Fo T  gram.  The 
calorific  value  of  -O^-Q  of  a  gram  of  hydrogen  is  -gV<nr  of  34460  =  4 
calories. 

One  cubic  centimeter  of  methane  (CEU)  has  approximately 
3  times  the  heating  value  of  1  cubic  centimeter  of  hydrogen  =  12 
calories.  One  cubic  centimeter  of  ethylene  (C2H4)  has  approxi- 
mately 5  times  the  heating  value  of  1  cubic  centimeter  of  hydro- 


22  COAL 

gen  =  20  calories.  Hence  for  this  condition  of  100  per  cent  excess 
air  the  losses  expressed  in  percentage  of  the  total  calorific  value 
of  a  fuel  are  as  follows: 

TJT  per  cent  of  hydrogen  in  the  flue  gas  =  ^\  per  cent  loss. 
TOO  per  cent  of  methane  in  the  flue  gas  =  J  per  cent  loss. 
per  cent  of  ethylene  in  the  flue  gas  =  f  per  cent  loss. 


The  determination  of  hydrogen,  methane  and  ethylene  in  the 
flue  gas  to  -TOT  per  cent  is  not  at  all  easy,  and  the  unaccounted- 
for  losses  due  to  traces  of  these  gases  in  some  cases  might  have 
appreciable  effects  on  the  heat  balances  without  the  chemist  in 
charge  being  able  to  determine  with  certainty  the  quantities  of 
these  gases  present. 

The  heat  loss  due  to  the  unburned  coal  in  the  soot  and  smoke 
usually  does  not  exceed  a  few  tenths  of  one  per  cent,  and  any 
serious  effect  due  to  this  cause  must  be  due  to  poor  absorption 
of  heat  by  the  boilers  as  a  result  of  deposition  of  soot  on  or  in  the 
tubes,  or  on  the  heating  surfaces. 

Water  added  to  dry  dusty  coal  to  wet  it  down  just  previous 
to  firing  may,  by  securing  more  favorable  conditions  of  firing, 
increase  the  available  heating  value  more  than  enough  to  counter- 
act the  heat  lost  by  the  evaporation  of  this  water  and  the  sensible 
heat  in  the  water  vapor.  However,  the  addition  of  any  water 
after  the  coal  is  actually  weighed,  in  so  far  as  the  heat  balance  is 
concerned,  simply  contributes  so  much  more  heat  as  latent  and 
sensible  heat  to  the  unaccounted  for  heat  losses.  Likewise  water 
added  to  the  ash  pit  may  by  its  cooling  action  on  the  grate  bars 
and  lower  part  of  the  fuel  bed  tend  to  improve  the  combustion 
of  the  coal  and  make  it  more  efficient.  In  so  far  as  the  heat  bal- 
ance is  concerned  this  sensible  and  latent  heat  is  also  included  in 
the  unaccounted-for  losses. 

The  sensible  heat  carried  off  by  the  moisture  in  the  air  used 
varies  with  the  excess  air  and  with  the  temperature  and  humidity 
of  the  air  ranging  from  less  than  0.1  per  cent  in  cold  dry  weather 
to  upwards  of  1  per  cent  of  the  total  heating  value  of  the  coal  in 
warm  rainy  weather.  For  example,  1  gram  of  Ohio  No.  6  coal 
(assuming  100  per  cent  excess  of  air)  requires: 

4}X[  (0.6903X1)  +  (0.0543X8)  +  (0.0330  XI)  -0.1362]  =  9.41 


COMPOSITION  AND  HEATING   VALUE  23 

grams  or  allowing  the  100  per  cent  excess  air  =  approximately  19 
grams  of  air  per  gram  of  coal  fired. 

19  grams  of  dry  air -14.7  liters  of  moist  air  at  0°  C.  (32°  F) 
760  mm.  or  =  17.0  liters  of  moist  air  at  30°  C.  (86°  F)  760  mm. 

One  liter  of  saturated  air  at  0°  C.  contains  4.8  mg.  of  water  vapor. 
One  liter  of  saturated  air  at  30°  C.  contains  30  mg.  of  water  vapor. 

14.7  liters  at    0°  C.  contains  70  mg.  of  water  vapor 
and 

17.0  liters  at  30°  C.  contains  510  mg.  of  water  vapor. 

The  sensible  heat  of  the  water  vapor  at  300°  C.  (572°  F.)  for 
the  two  conditions  is, 

0.070X0.48X300  =  10  calories 
0.510X0.48X270  =  66  calories 

a  loss  from  about  0.14  per  cent  to  about  1  per  cent,  from  which 
it  is  apparent  that  in  cold  or  dry  wreather  the  loss  is  quite  small, 
but  that  in  warm  rainy  weather  it  may  be  very  appreciable. 

Specific  heat  of  products  of  combustion.  The  exactness  of 
the  above  formulas  for  determining  the  available  heat  depends 
upon  the  exactness  of  the  values  for  the  specific  heats.  The 
specific  heats  of  the  gases  were  formerly  regarded  as  being 
practically  constant  for  all  temperatures,  but  more  recent  re- 
searches have  shown  that  changes  in  the  temperatures  of  the 
gases  are  accompanied  by  changes  in  the  specific  heats. 

The  mean  specific  heats  in  small  calories  per  gram  molecular 
volume  of  gases  under  constant  pressure  from  0°  Centigrade  to 
temperature  (t)  based  upon  the  results  of  Le  Chatelier  and 
Mallard  are  given  by  Damour1  substantially  as  follows: 

Diatomic  gases  (02,  N2,  H2  and  CO)  =6.83+0.0006  t. 
Water  vapor  (H2O)  =8.08+0.0029  t. 
Carbon  dioxide  (CO2)  =8.52+0.0037  t. 
Methane  (CH4)  =9.78+0.006  t. 

The  values  in  small  calories  per  gram  of  gas  or  in  kilograms 
calculated  per  kilogram  of  gas  under  constant  pressure  as  given 
by  Richards2  and  as  figured  from  the  formulas  given  above  are 
as  follows: 

1  Industrial  Furnaces.  2  Metallurgical  Calculations,  Vol.  I. 


24 


COAL 


RICHARDS. 


DAMOUR. 


Nitrogen 
Oxygen 
Water  vapor 
Carbon  dioxide 
Sulphur  dioxide 
Carbon  monoxide 
Hydrogen 
Methane 


=  0. 2405+0. 0000214* 
=  0.2104+0.0000187* 
=  0.42     +0.000185* 
=  0.19     +0.00011* 
'0.125  +0.0001* 
=  0. 2405  +0.0000214* 
=  3.37     +0.0003* 


0.2438+0.0000214* 
0.2135+0.0000187* 
0.447  +0.000162* 
0.194  +0.000084* 


0.2438+0.0000214* 
3.412  +0.000300* 
0.611   +0.000375* 


The  most  recent  values  for  specific  heats  of  the  common  gases 
are  given  by  Lewis  and  Randall1  and  are  based  mainly  upon  the 
work  of  Holborn  and  Austin,  Holborn  and  Henning  and  of  Pier. 
The  values  for  specific  heats  in  small  calories  per  gram  molecular 
volume  of  gas  under  constant  pressure,  for  absolute  temperatures 
are  as  follows: 

Nitrogen  =  6.50+0.0010T; 

Oxygen  =6.50+0.001071; 

Carbon  monoxide  =  6 . 50  +0 . 001077 ; 

Hydrogen  =6.50+0.0009^; 

Water  vapor  =8.81  -  0. 00 19T+0. 00000222  T72; 

Carbon  dioxide  =7.0+0.007171-0.00000186T2; 

Sulphur  dioxide  =  7.0+0.0071T-0.00000186T2. 

According  to  these  different  authorities  the  mean  specific 
heats  from  0  to  300°  Centigrade  (572°  Fahrenheit)  and  from  0 
to  1000°  Centigrade  (1832°  Fahrenheit)  for  these  different  gases 
are  as  follows : 


Richards 

Damour 

Lewis  and  Randall 

0  to  300 

0  to  1000 

0  to  300 

0  to  1000 

0  to  300 

0  to  1000 

Nitrogen          

0.247 
0.216 
0.223 
0.476 
0.247 
0.240 
0.155 

0.262 
0.229 
0.300 
0.605 
0.262 
0.257 
0.225 

0.250 

0.219 
0.219 
0.497 
0.250 
0.243 

0.265 
0.232 
0.278 
0.610 
0.265 
0.258 

0.247 
0.216 
0.219 
0.469 
0.247 
0.240 
0.150 
3.41 

0.259 
0.227 
0.248 
0.512 
0.260 
0.252 
0.170 
3.57 

Oxvffcn 

Carbon  dioxide 

Water  vapor    

Carbon  monoxide  

Air                                 

Sulphur  dioxide  

Hydrogen 

3.460 

3.670 

3.502 
0.723 

3.712 
0.986 

Methane              

The  specific  heat  of  ash  may  be  taken  as  about  0.16. 
1  Jr.  Am.  Chem.  Soc.  Vol.  XXXIV,  page  1128,  Sept.  1912. 


COMPOSITION  AND  HEATING   VALUE  25 

Calculation  of  the  available  heating  power  of  Hocking  or 
Ohio  No.  6  coal.  As  an  illustration  of  the  foregoing  calculations, 
the  available  calorific  value  of  this  coal  based  on  the  average 
analysis  of  the  seam  and  under  conditions  corresponding  to  the  use 
of  the  coal  in  a  steam  boiler  of  the  best  type  working  under  the  best 
conditions  is  calculated  as  follows:  The  excess  of  air  under  the 
conditions  assumed  is  taken  at  50  per  cent,  flue  temperature 
at  300°  C.,  temperature  of  the  air  at  zero  and  the  temperature 
at  which  the  ash  is  withdrawn  from  the  furnace  the  same  as  the 
temperature  of  the  air.  The  composition  and  the  calorific  value 
of  the  coal  are : 

Carbon 0 . 6903 

Hydrogen 0.0543 

Nitrogen 0 . 0126 

Oxygen 0 . 1362 

Sulphur 0.0330 

Ash . 0.0736 

Calorific  value 6980  Calories 

The  latent  heat  equals  9  X 0.0543  X  (539. 1+0.52(100))  =288.7 
The  water  equivalent  of  the  products  of  combustion  exclusive 
of  the  nitrogen  in  the  air  equals : 

Carbon  dioxide  =  0. 6903  x¥xO.  223  =  0.5644 
Water  =  0.0543X  9X0.476=0.2326 

Sulphur  dioxide  =0.0330X2   XO.  155  =0.0102 
Nitrogen  =0.0126X         0.247=0.0031 


0.8103 
The  oxygen  in  the  air  used  in  combustion  equals: 

For  carbon  =|X0.6903  =  1.8408 
For  hydrogen  =8X0. 0543  =  0 . 4344 
For  sulphur  =0.0330 


2.3082 
Deducting  the  oxygen  in  the  fuel  0 . 1362 


2.1720 


The  water  equivalent  of  the  nitrogen  in  the  air  corresponding 
to  the  oxygen  equals  3.33X0.247X2.1720  =  1.7865. 

The  water  equivalent  of  the  products  of  combustion,  0.8103, 
plus  the  water  equivalent  of  the  nitrogen  from  the  air,  1.7865, 


26  COAL 

equals  2.5968,  which  multiplied  by  300°,  the  flue  temperature- 
equals  779.0,  the  sensible  heat  carried  off  in  the  products  of  com, 
bustion. 

The  excess  air  equals  the  oxygen  (2.1720)  multiplied  by  4.33 
and  by  0.5  (the  ratio  of  excess  air),  or  2.1720X4.33X0.5  =  4.7024. 
The  heat  carried  off  in  the  excess  air  equals: 

4.7024X0.24X300°  =  338.6  heat  units. 

Writing  these  various  values  together  and  adding  them,  gives 
the  following: 

Latent  heat =  288.7 

Heat  lost  in  products  of  combustion  (including  nitrogen  from 

air  used) =  779 . 0 

Heat  lost  in  excess  air  in  flue  gas =  338 . 6 


Total.  . =1406.3 

Deducting  the  sum  (1406.3)  from  the  calorific  value  of  the 
fuel  '(6980)  leaves  5573.7  as  the  heat  theoretically  available  per 
unit  of  fuel  and  under  the  conditions  assumed.  This  is  equal 
to  about  80  per  cent  of  the  total  calorific  value. 

This  value  is  higher  than  the  actual  available  value  as  any 
heat  loss  due  to  unburned  coal  in  the  ash  pit  or  the  formation 
of  CO  instead  of  C02  and  the  radiation  losses  are  included  in  the 
80  per  cent.  Also  the  assumed  value  of  50  per  cent  for  the 
excess  air  is  much  lower  than  is  usually  found,  100  per  cent  excess 
being  a  closer  approximation  to  common  practice.  With  100 
per  cent  excess  air  and  the  same  flue  temperature,  300°  C., 
(572°  F.)  the  heat  loss  due  to  excess  air  is  338.6  calories  higher 
or  approximately  4.8  per  cent  of  the  total  heating  value.  Assum- 
ing 5  per  cent  for  unburned  coal  remaining  in  the  ash  pit,  or 
that  the  coal  actually  burned  equals  95  per  cent  of  the  coal 
fired  then  the  heat  lost  in  the  excess  air  and  in  the  products 
of  combustion  with  100  per  cent  excess  air  is  0.95  of  (1406.3  + 
338.6)  =  1657.6  calories  or  23.8  per  cent  of  the  total  heating 
value.  To  this  add  5  per  cent,  the  heat  in  the  unburned  coal,  = 
23.8+5  =  28.8  per  cent.  Then  100-28.8  =  71.2  per  cent  for 
evaporation  of  water  and  radiation  and  unaccounted-for  losses. 
If  the  radiation  and  unaccounted  for  losses  be  taken  as  10  per 
cent  the  remainder  available  for  actual  evaporation  of  water  = 


COMPOSITION  AND  HEATING   VALUE  27 

61.2  per  cent  of  the  total  heating  value.  61.2  per  cent  of  6980 
calories  =  4272  calories.  Dividing  this  number  by  539.1,  the 
latent  heat  of  evaporation  of  water  into  steam  at  100°  C.,  gives 
7.92  as  the  number  of  grams  of  water  that  can  be  evaporated 
by  one  gram  of  coal,  or  expressed  in  pounds  as  the  number  of 
pounds  of  water  that  can  be  evaporated  by  one  pound  of  coal. 

Printed  forms  for  calculating  the  heat  balance.  The  calcu- 
lation of  the  heat  balance  can  be  shortened  and  made  much  easier 
by  the  use  of  a  printed  form  for  entering  the  various  values  as 
determined  or  as  calculated.  Such  a  form  using  logarithms 
with  the  logarithms  of  the  constants  printed  on  the  form  saves 
much  labor  in  multiplying  and  dividing  and  once  familiar  with 
the  routine  the  calculation  is  comparatively  simple. 

On  pages  28-29  are  given  the  calculation  of  the  Ohio  No.  6 
coal  together  with  data  on  the  flue-gas  and  refuse  and  assuming 
that  the  refuse  is  removed  from  the  ash  pit  at  300°  C.  The 
values  for  the  specific  heats  corresponding  to  the  logarithms  used 
are  as  follows:  Nitrogen,  0.246;  oxygen,  0.215;  water  vapor,  0.48; 
carbon  dioxide,  0.217;  carbon  monoxide,  0.220;  air,  0.238;  sulphur 
dioxide,  0.15;  ash,  0.16. 

THE    USE    OF    THERMAL    CAPACITY    TABLES    FOR   HEAT 
CALCULATIONS 

The  use  of  thermal  capacity  tables  to  determine  the  sensible 
heat  carried  off  in  the  flue  gas  considerably  shortens  heat  balance 
calculations. 

By  thermal  capacity  of  a  gas  is  meant  the  heat  necessary 
to  raise  a  definite  quantity  of  the  gas  from  0°  C.  to  the  tem- 
perature (£).  The  tables  may  be  figured  on  any  basis  desired, 
as  the  thermal  capacity  per  liter,  per  molecular  volume  or  per 
cubic  foot,  or  the  thermal  capacity  per  kilogram,  gram  or 
pound,  or  as  in  the  table  given  the  thermal  capacity  of  the  gas 
corresponding  to  a  gram  of  one  of  the  elementary  constituents 
of  the  gas,  as  the  thermal  capacity  of  carbon  dioxide  per  gram 
of  carbon,  from  which  the  carbon  dioxide  is  derived.  The 
table  which  follows  is  on  the  basis  of  the  thermal  capacity  of  the 
several  gases,  produced  during  combustion,  corresponding  to 
one  gram  of  the  elements— carbon — hydrogen — sulphur  and 
nitrogen  in  the  coal.  The  value  for  air  is  per  gram  of  air. 


28 


GOAL 


HEAT  BALANCE  FOR  BOILER  TEST  WITH  COAL 


Analysis  of  Coal 

Vloisture  ....     5.56 
Vol.      Combusti- 
ble                       38   11 

C'  =  Carbon  in  coal  burned 
H'  =  Hydrogen  in  coal  burned 
O'  =  Oxygen  in  coal  burned 
S'  =  Sulphur  in  coal  burned 
N'  =  Nitrogen  in  coal  burned 

C"  =  Carbon  burned  to  CO 
C"'  =  Carbon  burned  to  CO2 

C'=C"+C'" 

Unburned   Coal=D 

ac 
r(l-a) 

a  =Ash  in  coal  by  analy- 
sis 
c  =Combustib'e  in  refuse 
r  =  Incombustible  in  ref- 
use 

(All  decimals) 
Log.  a                   =2.8669 
Log.  c                   =1  .6010 

Log.  ac                 =2  .4679 

Carbon  as  CO 

Log.  C' 
Log.  Q 

Fixed  Carbon    .   48.96 
Ash      7.36 

Log  C"         =.. 

C" 

Total.  .   .   .     100.  00 

Hydrogen    (H)       5.43 
Carbon         (C)      69.03 
Nitrogen      (N)       1.26 
Oxygen         (O)      13.63 
Sulphur        (S)        3.30 
Ash               (a)         7.36 

Total     ...     100.00 

Log.  C" 
Log.?            =0.3680 

O"  =Oxvgen  in  CO 
O'"=  Oxygen  in  CO2 
O'v  =  Oxygen  in  H2O 
Qv   =  Oxygen  in  SO2 

2O=O"+O'"+0'v+Ov 

SO  —  O'  =Oxygen  from  air 
used 
31  (  230  -0')=N"=  Nitrogen 
from  air  used 

Log.  CO        =  

T  ntr    PO 

Log.  r                    =7  .  775-9 
Log.  (1-a)          =1.9668 

Log.  Sp.  ht.=T-3424 

S   Log.       =  

Calorific  Value 

Calories     ....     6980 
B.T.U  12564 

Log.  r(l-a)        =7.7457 

W.  E.  CO      =            0 

Log.  ac                  =~2.4679 
(-)Log.  r(l-a) 
=  1.7457 

Heat  Loss  Due  to 
Formation  of  CO 

Log.  C" 
Log.  5650      =3.7520 
2  Log. 

Log.  D                 =8.7222 

Analysis  of  Refuse 

Combustible  (c)     39.9 
Refuse              (r)      60  .  1 

Total                  100.0 

Fvr,  -«  Air      °  (by  V°L> 

D                            =0.0527 
ID                    —0  9473 

o-° 

3-8-   *'-OS 
O=    10.60 

3V°  =   10.48 

Log.  (1-D)        =1.9765 

No.  Calories 
0 

Loss  Due  to  Unburned 
Coal 

Log.  D                  =2.7222 
Log.  cal.  value    =3.8439 

Oxygen  in  CO 

Log.  C" 
Log   £             =0.1249 

Analysis  of  Flue  Gas 

By  Vol. 
CO2       ....          0.4 
O2      ,                          10.6 

2  Log                —  2  5661 

Log.  O  =.7.02.53 
(-)Log-  (j^g-o)    =1.0204 

No.  Calories     =        ?.68 

Log.  O"         =  

CO        0.0 
N2   80.1 

0"                                0 

Total      .    .    .    100.0 

Ash 

Ash(l-D)            =0.0697 
D                            =0.0527 

Log.  Xs  Air                     =0.0040 

Carbon  as  CO2 

C'"=C'-C" 

Log.  C'"        =1.8155 
Log.  y            =0.5643 
Log.  Sp.  ht.    =1.3365 

Temperature 

Flue  Gases  (f)       =  300 

Log.  CO  (Vol.)  

Ash(l-D)+D    =  0^122_4 

Log.  Ash(l  -D)  +D 
=  /  .  0575 
Log.  Sp.  ht.          =1.2041 

S  Log.      =1.7163 

Log.  Q  =  

22  Log        —  2  ^919 

W.  E.  CO2     =0.524 

Water  Evaporated 
per  Ib.  coal            =7  .96 

Water  Evaporated  =W  =7.96 

Log.  W  =0.9009 
Log.  539.1  =2.7317 

W.  E.  Ash           =0.0197 

Oxygen  in  CO2 

Log.  C'"        «=  1.8  155 
Log.  §             =0.4259 

Carbon 

CO  (by  vol.) 

S  Log.  =8.6304 

Lo?.  (1-D)        =1.9765 

Log.  O"'        =0.^4/4 

No.  Calories                    =     4270 

Log.  C'                 =7.5/55 

0'"                    =1.744 

C0+C0»(hy  vol.) 

Note. — Where  the  amount  of    CO  present  in  the  flue  gas  is  small,  the    calculation  of    the  sensible 
heat  carried  off  by  CO  may  be  omitted,  and  in  calculating  the  heat  carried  oft  as  COa,  C'  taken  as  =C"'. 


COMPOSITION  AND  HEATING   VALUE 


29 


TEST  No. 


DATE. 


COAL  'Oiiio  No.  6" 


Hydrogen 
Log.  II                     =£.7348 
Log.  (1-D)             =1.9766 

Oxygen 

Log.  O                  =7.1341 

Water  Equivalent  of  Products  of  Combustion 

W.  E.  CO2       .     .                                       =0.6X4 
WP    PO                                                                   ^    /•"">'•> 

Log.  H'                     =~8J_!1§. 

Log.  O'                 =1  .1106 

W.  E.   H2O 

=  0.222 

Log.  H'                     =2.7113 
Log.  9                        =0.9542 
Log.  Sp.  h.               =1.6812 

O'                           =0.1290 

W.  E.  N2      
W.  E.  SO2        
W.  E.  Ash              

v 

Log.  S 
Log.  (t'-t)       

S  Log.         ....... 

.    -1.690 
=  0.009 
.    =0.020 

.    =2.465 

s  Log.               =L-A4^7- 

O"                                        0 

O'"                        =1.7440 
O'v                         =0.4116 
Ov                          =0.0312 

=0.3918 

.    =2.4771 

.    =2.8689 

W.  E.  H2O               =0.222 

Oxygen  in  H2O 

Log.  H'                     =2.7113 
Log.  8                       =0.9031 

SO                 =2.1868 

Log.  O'v                   -~L^1JA 

2O  -O'        =2.0578 

.       =        740 

O'v                            =0.4116 

31(20-0')         =N" 
Log.(  2O-OO    =0.3134 
Log.  31                  =0.5229 

Latent  Heat 
Log.  HaO                  =1.6655 
Log.(691.1-0.62t)=2.7717 

Log.  N"                =0.8363 

Heat  Balance 

Calories;      % 

S  Log.                    =*L4?Zf 

N"                         =0.50 

Latent  Heat            =       #?'-4 

Heat  in  Excess  Air 

Log.  (  2O-O')  =0.3134 
Log.  41                  =0.6368 

Sulphur 

Log.  S                       =2.5185 
Log.  (1-D)             =1.9765 

Log.  S'                      =~2.4950 

Latent  Heat   ....                 i 
Products  of  combustion 
Excess  Air                                             < 

174            3.9 
?40         10.6 
144            9  .  3 
0            0.0 
168            5.3 
>70          61.2 
•84            9.7 

Log.  Air                =0.9502 

Log.  S'                     =2.4950 
Log.  2                        =0.3010 
Log.  Sp.  ht.             =1.1761 

Log.  Air                =0.9502 
Log.  Xs  Air         =0.0049 
Log.  Sp.  ht.         =  1  .  3766 

Log.  (t'-t)          =18.4771 

CO        

Unburned  coal      ...                  t 
Water  evaporated      .       .                4- 
Loss      i 

SLog.                  =3.9721 

Total     ,      1    6i 

W6~    100.0 

W.  E.  SO2                =0.0094 
Ov  =S'                     =0.0312 

S  Log.             =2.8038 

No.  Calories        =        0^4 

Nitrogen 
Log.  N                     =2.1004 
Log.  (1-D)             =1.9766 

Total  heat  carried  off  by  H2O  in  gases  = 

f  (100  —  t)  =the  heat  required  to  raise  water  to  100°  C. 
•1  539.  1  =the  latent  heat  of  vaporization  at  100°  C. 
[0.48(f  —  100)  the  sensible  heat  in  water  vapor  from  100°  to  t'. 

This  may.be  written 

0.52(100  -t)  +0.48(100  -t)  +639.1  +0.48  (f  -100)  =\539.1  +0.52(100  -t)] 
+0.48(t'  -t)  =691  .  1  -0.52t(the  latent  heat)  +0.48(t'  -t)  the  sensible 
heat  in  water  vapor  from  t  up  to  t'. 

Log.  N'                     =~2.0769 

N'                               =0.0119 
N"                            *=0.*0 

S                         =6.872 

Log.  S                       =0.8371 
Log.  Sp.  ht.              =  1  .  3909 

S  Log.                        =0_._2280 

W.  E.  N2                  =7.55 

If  0.01  of  the  carbon  burns  to  CO  and  is  calculated  to  CO2  instead,  the  error  introduced  in  sensible 
heat  is  about  5.6  cal.  where  flue  gas  is  200°  C.  above  boiler-room  temperature. 


30 


COAL 


THERMAL  CAPACITY  FROM  0°  C.  TO  TEMPERATURE  (t) 

VALUES  IN  SMALL  CALORIES 


d 

d 

. 

0 

d 

d 

c 

d 

,d 

"o 

0 

o 

"8  d 

"8  c 

0 

*8  3 

0 

d         M 

UH 

0 

si* 

i 

m 

a 

V 

ft 

111 

a 

i 

a 

25 

*O<! 

•M 

ss 

IM 

n'OO 

IM 

0OO 

M-j 

«Ooo 

<*j 

K  osW 

«*^ 

H 

< 

Q 

52 

Q 

O 

Q 

0 

Q 

§ 

Q 

o 

Q 

32 

0 

50 
'  68 
86 
104 
122 
140 
158 
176 
194 
212 
230 
248 
266 
284 
302 
320 
338 
356 
374 
392 
410 
428 
446 
464 
482 
500 
518 
536 
554 
572 
590 
608 
626 
644 
662 
680 

10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
110 
120 
130 
140 
150 
160 
170 
180 
190 
200 
210 
220 
230 
240 
250 
260 
270 
280 
290 
300 
310 
320 
330 
340 
350 
360 

2.37 
4.74 
7.12 
9.50 
11.89 
14.28 
16.67 
19.07 
21.48 
23.88 
26.30 
28.71 
31.13 
33.56 
35.98 
38.42 
40.85 
43.29 
45.73 
48.19 
50.64 
53.09 
55.55 
58.02 
60.49 
62.97 
65.44 
67.92 
70.41 
72.90 
75.40 
77.89 
80.39 
82.90 
85.42 
87.93 

0.237 
0.238 
0.238 
0,239 
0.239 
0.239 
0.240 
0.241 
0.241 
0.242 
0.242 
0.242 
0.243 
0.243 
0.244 
0.244 
0.244 
0.244 
0.245 
0.245 
0.245 
0.246 
0.247 
0.247 
0.248 
0.248 
0.248 
0.249 
0.249 
0.250 
0.250 
0.250 
0.251 
0.251 
0.251 

2.44 
4.88 
7.33 
9.78 
12.24 
14.70 
17.17 
19.64 
22.11 
24.59 
27.07 
29  .  56 
32.05 
34.55 
37.05 
39.55 
42.06 
44.57 
47.08 
49.61 
52.13 
54.66 
57.20 
59.74 
62.28 
64.83 
67.37 
69.93 
72.48 
75.05 
77.62 
80.19 
82.77 
85.35 
87.94 
90.53 

0.244 
0.245 
0.245 
0.246 
0.246 
0.247 
0.247 
0.247 
0.248 
0.248 
0.249 
0.249 
0.250 
0.250 
0.250 
0.251 
0.251 
0.251 
0.252 
0.252 
0.253 
0.254 
0.254 
0.254 
0.255 
0.255 
0.256 
0.256 
0.257 
0.257 
0.257 
0.258 
0.258 
0.259 
0.259 

7.1 
14.3 
21.6 
28.9 
36.3 
43.7 
51.2 
58.8 
66.4 
74.1 
81.8 
89.6 
97.5 
105.4 
113.4 
121.5 
129.6 
137.8 
146.0 
154.3 
162.7 
171.1 
179.6 
188.1 
196.9 
205.6 
214.2 
222.9 
231.8 
240.7 
249.7 
258.8 
267.9 
277.0 
286.3 
295.5 

0.72 
0.73 
0.73 
0.74 
0.74 
0.75 
0.76 
0.76 
0.77 
0.77 
0.78 
0.79 
0.79 
0.80 
0.81 
0.81 
0.82 
0.82 
0.83 
0.84 
0.84 
0.85 
0.85 
0.87 
0.87 
0.87 
0.87 
0.89 
0.89 
0.90 
0.91 
0.91 
0.91 
0.92 
0.92 

5.7 
11.6 
17.1 
22.9 
28.6 
34.3 
40.1 
45.9 
51.6 
57.4 
63.2 
69.0 
74.8 
80.6 
86.5 
92.4 
98.2 
104.1 
110.0 
115.8 
121.7 
127.6 
133.6 
139.5 
145.4 
151.4 
157.3 
163.3 
169.3 
175.3 
181.3 
187.3 
193.3 
199.3 
205.3 
211.4 

0.55 
0.55 
0.56 
0.57 
0.57 
0.58 
0.58 
0.58 
0.58 
0.58 
0.58 
0.58 
0.58 
.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.59 
0.60 
0.60 
0.60 
0.60 
0.60 
0.60 
0.60 
0.60 
0.60 
0.60 
0.61 

2.5 
5.1 
7.7 
10.4 
13.1 
15.8 
18.6 
21.5 
24.4 
27.3 
30.2 
33.2 
36.3 
39.4 
42.5 
45.6 
48.8 
52.1 
55.4 
58.7 
62.1 
65.5 
69.0 
72.6 
76.0 
79.6 
83.2 
86.9 
90.6 
94.4 
98.2 
102.0 
105.9 
109.8 
113.8 
117.8 

0.26 
0.26 
0.27 
0.27 
0.27 
0.28 
0.29 
0.29 
0.29 
0.29 
0.30 
0.31 
0.31 
0.31 
0.31 
0.32 
0.33 
0.33 
0.33 
0.34 
0.34 
0.35 
0.35 
0.35 
0.36 
0.36 
0.37 
0.37 
0.38 
0.38 
0.38 
0.39 
0.39 
0.40 
0.40 

40.6 
81.4 
122.5 
163.9 
205.6 
247.6 
289.9 
332.5 
375.3 
418.5 
462.0 
505.6 
549.7 
594.0 
638.6 
683.8 
728.7 
774.1 
819.9 
866.0 
912.3 
958.9 
1005.9 
1053.1 
1100.6 
1148.4 
1196.5 
1244.9 
1293.5 
1342.5 
1391.7 
1441.2 
1491.1 
1541.2 
1591.6 
1642.3 

4.08 
4.11 
4.14 
4.17 
4.20 
4.23 
4.26 
4.28 
4.32 
4.35 
4.36 
4.41 
4.43 
4.46 
4.49 
4.52 
4.54 
4.58 
4.61 
4.63 
4.66 
4.70 
4.72 
4.75 
4.78 
4.81 
4.84 
4.86 
4.90 
4.92 
4.95 
4.99 
5.01 
5.04 
5.07 

1°  F.  =5°  C.     (°  C.  Xs)+32=°  F. 

1°  C.  =j}°F.     (°  F-32)  X§=°  C. 

To  determine  the  heat  necessary  to  raise  a  gas  from  temper- 
ature t  to  t'  by  means  of  a  thermal  capacity  table,  the  thermal 
capacity  of  the  gas  at  t  is  subtracted  from  the  thermal  capacity 
of  the  gas  at  t'.  For  example,  the  heat  required  to  raise  1  gram 
of  air  from  20°  C.  to  320°  C.  is  the  difference  between  the  thermal 
capacity  at  320°  C.  and  the  thermal  capacity  at  20°  C.  =  77.89 
-4.74  =  73.15  calories.  In  ordinary  boiler  test  calculations 
his  value  can  be  obtained  with  sufficient  accuracy  by  simply 


COMPOSITION  AND  HEATING   VALUE 


31 


taking  the  thermal  capacity  of  the  gas  corresponding  to  the 
difference  in  temperature.  320°  C.  minus  20°  C.  =  300°  C., 
and  the  thermal  capacity  of  the  gas  at  300°  C.  by  the  table  is 
72.90  as  against  the  more  exact  figure  73.15,  an  agreement  suf- 
ficiently close  to  warrant  the  use  of  the  abbreviated  method 
in  most  calculations. 

The  calculation  of  No.  6  coal  using  the  data  on  the  logarithmic 
form  and  the  thermal  values  using  the  table  of  thermal  capac- 
ities is  as  follows: 

The  unburned  coal  is  0.0527  from  which  l—d  =  0.9473. 
The  values  of  the  different  constituents  in  the  coal  burned  for  a 
unit  of  coal  as  fired  are  as  follows; 


Carbon 0 . 6903 

Hydrogen 0.0543 

Nitrogen 0.0126 

Oxygen 0 . 1362 

Sulphur 0.3330 

Ash. .  .  0.0736 


X(l-d)     or    0.9473  = 


C'= 0.6539 
H'=0.0514 
N'=0.0119 
O'  =0.1290 
S' =0.0312 
A' =0.0697 


The  latent  heat  =  9 X0.0514X (539.1  +0.52  (100))  =274. 
The  sensible  heat  of  the  products  of  combustion  using  the 
thermal  capacity  values  of  the  gases  for  300°  equals: 

For  carbon  dioxide      =  0 . 6539  X  240 .7  =157.0 

For  carbon  monoxide  =  0 . 0000  X 

For  water  =0.0514X1342  =   69.0 

For  sulphur  dioxide    =0.0312X94.4  =     3.0 

For  nitrogen  =0.0119.     (See  below) 

The  sum  =229.0. 

The  oxygen  required  for  carbon  dioxide  =  0.6539Xf  =1.7437 
The  oxygen  required  for  water  =0.0514X8=0.4112 

The  oxygen  required  for  sulphur  dioxide  =0.0312 XI  =0.0312 


Total 

Deducting  the  oxygen  in  the  fuel 
The  oxygen  from  the  air  required 


=  2.1861 


0.1290 


'  2. 0571 


The  nitrogen  corresponding  to  the  oxygen  =  3. 33X2.057  =  6. 85. 
To    this    add    the    nitrogen    in    the    coal,    0.0119  =  6.862.     The 


32 


COAL 


sensible  heat  in  the  nitrogen  using  the  thermal  value  for  300° 
=  6.862X75.05  =  515.0. 

The  excess  air  =  4. 33 X oxygen  required  (2.057)X1.01,  the 
ratio  of  the  excess  air  =  8.996. 

The  sensible  heat  in  the  excess  air  =  8. 996  X  thermal  capacity 
of  air  for  300°  =  8.996X72.90  =  656. 

The  sensible  heat  of  the  refuse  =  [the  ash  (0.0697) +the 
unburned  coal  (0.0527)] X0.16  (the  specific  heat)X300  =  5.9 

The  heat  lost  due  to  the  formation  of 


CO  =  C'X 


CO 


CO+CO2 


X  5650  =  000.0 


The  heat  lost  in  unburned  coal  =  0.0527X6980  =  368.0. 
The    heat    of    the     water     evaporated  =  7.92X539. 1=4270.0 
The  summary  of  the  heat  balance  is  as  follows: 


Calories. 

Per  Cent. 

Latent  heat                

274 

3  9 

Products  of  combustion  (including  refuse)  
Excess  air 

747 
656 

10.7 
9  4 

Carbon  monoxide              

000 

0  0 

Unburned  coal    

368 

5  3 

\Vatp7  evaporated 

4270 

61  2 

Radiation  etc                           

665 

9  5 

Total 

6980 

100  0 

The  values  obtained  for  the  losses  in  the  products  of  com- 
bustion and  in  the  excess  air  are  7  and  12  calories  higher  than 
those  obtained  by  use  of  the  logarithmic  form.  A  portion  of 
this  difference  is  due  to  the  use  of  the  log  tables  but  the  greater 
portion  is  due  to  the  differences  in  the  values  taken  for  specific 
heats,  the  values  used  on  the  logarithmic  form  differing  some- 
what from  Damour's  values  which  are  used  in  the  thermal 
capacity  table.  The  differences  are  not  large,  but  are  sufficient  to 
call  attention  to  the  fact  that  the  actual  results  obtained  depend 
upon  the  particular  constants  used. 

To  change  calories  into  B.t.u.,  it  is  only  necessary  to  multiply 
each  item  in  calories  by  |  to  obtain  the  equivalent  value  in 
B.t.u.  The  percentage  relations  are  unchanged. 


COMPOSITION  AND  HEATING  VALUE  33 

Balance  on  basis  of  coaL  fired.  The  heat  balance  as  given 
is  based  on  the  amount  of  coal  actually  fired  under  the  boiler. 
From  this  balance  the  calculation  to  any  basis  desired  is  com- 
paratively easy. 

(I)'  Per  pound  of  dry  coal  fired.  To  obtain  the  values  per 
pound  of  dry  coal  fired,  divide  the  values  per  pound  of  coal 
fired  by  (1  — the  moisture  in  the  coal). 

(2)  Per    pound    of   combustible  fired.     (Combustible    by    the 
Mechanical    Engineering   Code   definition  =  l  — (moisture + ash)). 
To  obtain  the  values  per  pound  of  combustible  fired,  divide  the 
values  per  pound  of  coal  fired  by  1  —  (moisture + ash). 

(3)  Per  pound  of  coal  burned.     To  obtain  the  values  per  pound 
of  coal  burned  omit  the  item  of  unburned  coal  and  divide  the 
remaining  items  per  pound  of  coal  fired  by  (1  — the  unburned 
coal).     Reduce  to  a  basis  of  100  per  cent. 

(4)  Per  pound  of  dry  coal  burned.     Omit  the  item  of  unburned 
coal  and  divide  the  remaining  items  per  pound  of  coal  fired  by 
[(1— the  moisture)  X(l  — the  unburned  coal)].     Reduce  to  a  basis 
of  100  per  cent. 

(5)  Per    pound    of   combustible    burned.     Omit    the    item    of 
unburned  coal  and  divide  the  other  values  per  pound  of  coal 
fired  by  [[1  —  (moisture + ash)] X  (1  —  the  unburned  coal)].    Reduce 
to  a  basis  of  100  per  cent. 

For  purposes  of  comparing  different  values,  or  compar- 
ing boiler  efficiency,  some  of  these  modified  forms  are  desirable, 
but  there  appears  no  valid  reason  for  not  making  the  i:  coal 
as  fired  "  the  primary  basis.  Certainly  the  consumer  testing 
out  two  coals  needs  this  basis  as  he  pays  for  the  coal  in  the  ash 
pit  just  the  same  as  for  that  which  is  burned  and  a  report  of  a 
balance  omitting  the  item  of  unburned  coal  is  hardly  to  be  con- 
sidered as  complete. 

The  foregoing  heat  balance  in  its  essential  details  has 
been  used  in  the  Departments  of  Metallurgy  and  Mechan- 
ical Engineering  at  the  Ohio  State  University  for  the  past 
fifteen  years  and  graduates  of  these  departments  who  conduct 
boiler  tests  are  consistently  using  heat  balance  forms  based 
on  these  principles.  The  mechanical  engineering  profession,  in 
general,  has  not  given  this  basis  of  calculation  the  considera- 
tion that  it  deserves,  but  has  continued  to  use  the  older  code 
form. 


34  COAL 

The  Code  balance  recommended  by  the  American  Society 
of  Mechanical  Engineers  is  based  on  the  combustible  actually 
burned.  The  distribution  of  the  items  is  as  follows: 


HEAT  BALANCE  OR  DISTRIBUTION  OF  THE  HEATING  VALUE  OF  THE 
COMBUSTIBLE 

Total  Heat  Value  of  1  Pound  of  Combustible  B.t.u.     Per  Cent. 

1.  Heat  absorbed  by  the  boiler  =  evaporation  from  and  at 

212°  per  pound  of  combustible X 965. 7 

2.  Loss  due  to    moisture  in  coal  =  per  cent  of  moisture  re- 

ferred to  combustible  divided  by  100  X  [ (2 12 -t +966  + 
0.48(T-212)]  (t=  temperature  of  air  in  the  boiler 
room,  T  =  that  of  the  flue  gases.) 

3.  Loss  due  to  moisture  formed  by  the  burning  of  hydrogen 

=  per  cent  of  hydrogen  to  combustible  divided  by 
100X9X[(212-0+966+0.48(T-212)] * 

4.  Loss  due  to  heat  carried  away  in  the  dry  chimney  gases  = 

weight  of  gas  per  pound  of  combustible X0.24(T— £) 

5.  Loss  due  to  incomplete  combustion  of  carbon  = 

CO      ..per  cent  C  in  combustible 

co2+cox  ~loo~~ 

6.  Loss  due  to  unconsumed  hydrogen  and  hydrocarbons,  to 

heating  the  moisture  in  the  air,  to  radiation,  and  un- 
accounted for 


Totals 100.00 

A  comparison  of  the  items  given  in  the  heat  balance  of  the 
coal  as  fired  with  the  items  of  the  Code  balance  is  as  follows: 

Item.  Balance  Coal  as  Fired.  Code  Balance. 

No.  1.  Latent  heat  corresponds  to  Nos.  2  and  3 

No.  2.  Sensible  heat  in  products  of  combustion  corresponds  to  part  of  Nos.  2, 

3,  and  4 
No.  3.  Heat  in  the  excess  air  corresponds  to  remainder    of 

No.  4 

No.  4.  Heat  lost  due  to  CO  corresponds  to  No.  5 

No.  5.  Loss  due  to  unburned  coal  not  included 

No.  6.  Heat  in  the  water  evaporated  corresponds  to  No.  1 

No.  7.  Radiation  and  other  losses  corresponds  to  part  of  No.  6 

A  balance  to  be  satisfactory  should  show  where  all  the  heat 
goes  and  should  separate  the  variable  heat  losses  into  separate 
items  in  order  that  the  magnitude  of  each  can  be  readily  appre- 
ciated. In  this  respect  the  enumeration  of  the  heat  lost  in 
the  unburned  coal  and  the  heat  lost  in  the  excess  air  as  separate 


COMPOSITION  AND  HEATING   VALUE 


35 


items  is  a  decided  improvement  over  the  code  form.  The 
separation  of  relatively  fixed  losses  from  the  more  variable  ones 
is  certainly  desirable  in  order  to  more  clearly  appreciate  the 
magnitude  of  the  variable  losses,  as  loss  due  to  too  much  air 
compared  to  the  loss  from  formation  of  CO  due  to  too  little  air 
or  the  losses  in  sensible  heat  for  different  temperatures  of  the 
flue  gases  and  different  percentages  of  excess  air.  For  example, 
what  are  the  losses  in  burning  Ohio  No.  6  (Hocking)  Coal  with  50 
per  cent  excess  air  and  0.2  per  cent  of  CO  in  the  flue  gas  and  a 
flue  temperature  of  350°  C.;  or  with  150  per  cent  excess  air  and 
no  CO  in  the  flue  gas  at  temperatures  of  200  and  300°  compared 
with  the  given  conditions  of  100  per  cent  excess  air,  no  CO  and 
a  temperature  of  300°  C?  These  conditions  as  to  excess  air 
correspond  to  flue  gas  analyses  as  follows: 


ANALYSIS  OF  FLUE  GASES  WITH  VARYING  EXCESS  AIR 


50  Per  Cent. 

100  Per  Cent. 

150  Per  Cent. 

CO2  
02  
CO  

12.7 
7.0 
0.2 

9.5 
10.4 
0.0 

7.4 
12.5 
0.0 

N2 

80  1 

80  1 

80  1 

100.0 

100.0 

100.0 

The  carbon    burned    to  CO  with  50    per  cent  excess  air  is 
CO  2 

==^"^'     ^'^  °^  ^-6538  (the   car^on  burned  per 


unit  of  coal  fired)  =0.01  gram  per  gram  of  coal  fired. 

The  calculated  losses  with    the    different  conditions    are   as 
follows  : 

100  per  cent  excess  air,  300°  C.,  0  per  cent  CO 

Products  of  combustion  =  /as  already  calculatedX   740 
Excess  air  .............  =  I  in  the  heat  balance.  I  644 

CO  ..................  =  \See  log  sheet.  /       0 


Total. 


1384 


36  COAL 

50  per  cent  excess  air,  350°  C.,  0.2  per  cent  CO 

350 

Products  of  combustion  =  740 X— -  =  863 

oOO 

350 

Excess  air =  644X^X^-  =376 

oOO 

CO..  .=0.01X0.5650=  57 


Total 1296 

150  per  cent  excess  air,  200°  C.,  0  per  cent  CO 

Products  of  combustion  =  740  X —  =493 

oUU 

200 

Excess  air =  644Xf  X--  =644 

oOO 

CO.. 


Total 1147 

150  per  cent  excess  air,  300°. C.,  0  per  cent  CO 

300 

Products  of  combustion  =  740  X —  =740 

oUU 

Excess  air =644Xf  = =  966 

oOO 

CO.. 


Total 1706 

These  widely  divergent  values  serve  to  show  the  importance 
of  a  proper  relation  of  excess  air  to  flue  temperature  and  the 
importance  of  having  the  heat  balance  stated  in  such  a  form  as 
to  admit  of  a  ready  comparison  of  these  losses. 

Variation  of  available  heating  power.  The  available  heating 
power  of  a  coal  as  used  under  a  boiler  is  greatly  modified  by  the 
adaptability  of  the  coal  to  burn  on  the  particular  grate  and  in 
the  particular  furnace  used.  Coals  differ  in  the  percentage  of 
the  excess  of  air  required  for  their  complete  combustion  and  it 
is  well  known  that  experience  in  the  use  of  any  coal  is  necessary 
to  use  it  to  the  best  advantage.  Coals  which  contain,  or  furnish 
on  burning,  large  percentages  of  water  will  show  low  percentages 


COMPOSITION  AND  HEATING   VALUE  37 

of  available  heat  calculated  on  their  total  calorific  value  on 
account  of  the  large  amount  of  the  latent  heat  and  the  large 
quantity  of  sensible  heat  carried  off  by  the  water  vapor  in  the 
products  of  combustion.  As  has  just  been  shown,  the  amount 
of  sensible  heat  carried  off  in  the  products  of  combustion  increases 
directly  with  the  temperature  of  the  escaping  gas  and  the  best 
results  for  available  heating  power  are  usually  not  secured  where 
the  flue  temperature  is  excessive.  This  is  especially  true  where 
the  amount  of  moisture  in  the  coal  is  large.  The  amount  of 
ash  present  in  the  coal  has  an  important  effect  on  the  available 
heating  power  realizable  as  complete  combustion  and  low  excess 
air  are  hard  to  obtain  with  high  ash  or  where  the  ash  clinkers 
badly.  Aside  from  its  effect  on  the  excess  air  and  complete 
combustion,  large  amounts  of  ash  involve  extra  expense  in 
handling  and  on  this  account  have  a  negative  heating  value. 
The  loss  of  heat  due  to  formation  of  smoke  and  soot  varies  with 
the  coal  used  and  also  with  the  type  of  furnace,  but  the  actual 
loss  from  this  cause  is  in  no  case  very  large  and  coals  which 
have  a  tendency  to  form  large  amounts  of  smoke  and  soot  are 
objectionable,  more  on  account  of  being  a  nuisance  and  a  menace 
to  public  health,  or  because  the  deposition  of  soot  on  the  heat 
absorbing  surfaces  of  the  boiler  prevents  the  ready  absorption 
of  heat  by  the  boiler  rather  than  on  account  of  the  loss  of  heat 
due  to  failure  of  the  smoke  and  soot  to  burn, 

COMMERCIAL  VALUE   OF  COAL 

For  most  purposes  the  relative  commercial  value  of  a  coal  is 
dependent  upon  the  amount  of  heat  or  power  which  can  be  obtained 
from  a  given  amount  of  the  coal,  or  in  other  words  is  dependent 
upon  the  available  heating  value  of  the  coal.  In  most  cases  the 
available  heating  value  varies  directly  with  the  total  heating 
value,  and,  other  things  being  equal,  the  value  of  a  coal  is 
dependent  upon  the  total  number  of  heat  units  it  contains.  This 
is  however  not  always  the  case.  A  number  of  factors,  some 
of  which  have  already  been  mentioned,  as  clinkering  of  ash, 
adaptability  of  one  coal  rather  than  another  to  the  furnace  and 
stokers  in  use,  etc.,  may  cause  the  total  value,  if  considered  alone, 
to  be  somewhat  misleading  and  some  coals  having  a  lower  total 
calorific  value  may  under  certain  conditions  of  practice  give 


38  •    COAL 

a  higher  actual  available  value  than  other  coals  showing  a 
greater  total  value. 

In  general,  however,  the  coal  having  higher  total  healing  value 
is  the  better  coal  and  the  seller  of  the  coal  having  the  lower  heating 
value  should  show  under  what  special  conditions  an  inherently 
inferior  coal  may  actually  be  the  superior  coal  in  production  of 
heat  or  power,  or  if  not  actually  superior,  show  that  it  actually  is 
the  more  desirable  coal  under  the  conditions  where  it  is  to  be  used. 

Actual  testing  under  average  working  conditions  is  sometimes 
necessary  to  prove  or  disprove  the  claim  of  any  certain  coal.  A 
comparison  of  the  results  of  a  boiler  test  made  by  experts  under  the 
best  obtainable  conditions  with  the  every-day  results  of  the  ordi- 
nary boiler  crew  is  not  the  way  to  prove  or  disprove  it,  but  only 
shows  that  the  average  conditions  may  be  far  from  satisfactory. 
The  boiler  tests  if  taken  as  a  guide  should  be  made  on  both  coals 
and  under  similar  working  conditions.  The  average  results  for  a 
considerable  period  of  time  on  one  coal  compared  with  the  average 
results  on  another  coal  for  the  same  length  of  time,  if  conditions 
of  firing,  weather  conditions,  etc.,  are  similar  ought,  to  be  con- 
clusive as  to  which  coal  is  better  under  the  same  conditions.  This 
does  not  necessarily  show  how  much  better  either  coal  might  be 
if  the  firing  and  regulations  were  as  good  as  they  should  be. 
Boiler  tests  with  expert  handling  should  show  what  maybe  done; 
how  nearly  every-day  results  can  come  to  this  is  largely  depen- 
dent upon  the  efficiency  of  the  boiler  crew. 

RESIDUAL  COAL 

If  the  variable  factors  of  coal,  moisture,  ash  and  sulphur, 
be  removed  the  remainder  may  be  considered  as  consisting  of  a 
practically  uniform  residual  coal  substance  which  while  complex 
in  its  nature  is  fairly  uniform  in  composition  and  heating  value. 
The  value  of  the  coal  actually  bought  and  sold  is  largely  depen- 
dent upon  the  actual  percentage  of  residual  coal  present.  In  any 
given  seam  the  heating  value  of  a  unit  amount  of  the  residual 
coal  is  fairly  constant  and  different  samples  of  coal  from  the 
same  bench  or  seam  will  differ  from  one  another  in  heating  value 
according  as  they  differ  in  the  amounts  of  moisture,  ash  and  sul- 
phur present,  or  stated  in  another  way,  as  they  differ  in  the 
amount  of  actual  "  residual  coal  "  present  in  a  unit  amount  of  each. 


COMPOSITION  AND  HEATING   VALUE  39 

Heating  value  of  residual  coal,  H.  The  heating  value  of  a 
unit  weight  of  the  residual  coal  was  designated  by  the  late  Pro- 
fessor N.  W.  Lord  as  H  and  is  found  as  follows: 

From  the  total  heating  value  of  the  sample  subtract  that 
due  to  the  sulphur  present  which  equals  the  amount  of  sulphur 
times  2250  calories  or  times  4050  British  thermal  units.  Divide 
the  remainder  by  1  minus  the  sum  of  the  amount  of  moisture, 
ash  and  sulphur  present.  The  product  is  the  heating  value  per 
unit  of  residual  coal,  or 

„_  calorific  value  —  2250  (sulphur) 
1  —  (moisture  +  ash  +  sulphur) 

The  average  of  65  samples  of  Ohio  No.  6  coal  as  given  in 
Bulletin  No.  9  of  the  Ohio  Geological  Survey  is  as  follows: 

Moisture  .............................  0.0556 

Ash  .................................  0.0736 

Sulphur  ..........  .  ...................  0.0330 

Calorific  value  ........................  6980  calories 

from  which, 

„  6980-0.0330X2250 


or  expressed  in  British  thermal  units, 

8243X1  =  14837. 

Calculation  of  heating  value  from  proximate  analysis  and 
from  H.  Since  the  heating  value  of  the  coal  is  due  to  the  residual 
coal  and  sulphur  present,  the  heating  value  of  one  sample  may 
be  calculated  from  the  determined  heating  value  of  another  sample 
if  the  moisture,  ash  and  sulphur  in  both  samples  are  known.  For 
example,  to  calculate  the  heating  value  of  a  sample  of  Ohio  No. 
6  coal,  Sample  No.  115  of  Bulletin  No.  9  of  the  Ohio  Geological 
Survey  contains, 

Moisture  .............................  0  .  0472 

Ash  .................................   0.0547 

Sulphur  ..............................  0  .  0405 

The  amount  of  residual  coal 

=  1  -  (0.0472+0.0547+0.0405)  =0.8576. 


40  COAL 

Multiplying  the  value  of  H  above  —  8243  —  by  this  value 
=  8243X0.8576  =  7069  whfich  is  the  heat  of  the  residual  coal. 
To  this  add  the  heat  due  to  the  sulphur  =  0.0405X2250  =  91 
calories.  The  total  heating  value  =  7069  +91  =  7160.  The  calo- 
rific value  as  actually  determined  was  7199  or  a  difference  of  39 
calories. 

Accuracy  of  calculated  heating  value.  Where  the  samples 
from  which  H  is  determined  are  from  the  same  portion  of  the 
seam  as  the  sample,  the  heating  value  of  which  is  to  be  determined, 
and  where  the  variations  in  moisture,  ash  and  sulphur  are  not  too 
large  the  calculated  results  agree  fairly  well  with  actual  determin- 
ations. 

Results  for  heating  value  calculated  on  oxidized  and  weathered 
samples  are  likely  to  be  much  too  high,  and  it  is  unsafe  to  apply 
this  calculation  to  such  samples. 

Results  on  widely  different  samples.  As  it  is  difficult  or 
impossible  to  determine  the  exact  relation  of  the  ash  obtained  to 
the  amount  of  mineral  matter  as  it  occurs  in  the  coal  where  the 
variations  in  ash  and  sulphur  are  large,  the  results  by  this  formula 
may  be  considerably  in  error. 

Effect  of  changes  in  ash  on  accuracy  of  calculation.  As  pre- 
viously stated  under  the  subject  of  "  Ash,"  the  ash  as  actually 
weighed  is  too  high  by  f  of  1  per  cent  for  each  per  cent  of  sul- 
phur in  the  coal  as  pyrite,  and  too  low  by  about  0.17  of  1  per  cent 
for  each  per  cent  of  ash  originally  present  in  the  coal  as  clay  or 
shale.  Where  the  differences  in  ash  and  sulphur  in  the  different 
samples  are  due  to  differences  in  amounts  of  clay  and  pyrite, 
application  of  this  formula  in  a  modified  form,  using  a  "  corrected 
ash  "  for  the  difference  in  ash  in  the  two  samples,  gives  more  con- 
cordant results.  Designating  the  amounts  of  ash  and  sulphur 
in  the  samples  from  which  H  has  been  determined  as  A  and  S 
and  the  amounts  of  ash  and  sulphur  in  the  samples  the  calorific 
value  of  which  is  to  be  determined  by  A'  and  Sf,  then  the  ash 
corrected  or  A'  (corrected)  = 


from  which  the  corrected  ash  in  Sample  No.  115  corresponding  to 
0.0547  =  0.0547  -  f  (0.0405  -0.0330)  +  .17(0.0547  -  0.0736  -  f  (0.0405 


COMPOSITION  AND  HEATING   VALUE 


41 


-0.0330)]  =0.0482  or  0.0065  less  ash  than  the  amount  as  actually 
weighed  up.  Using  this  corrected  value  gives, 

1- (0.0472+0.0482+0.0405)  =0.8641 

as  the  amount  of  residual  coal  as  against  0.8576  by  the  first 
calculation.  The  calorific  value  of  the  sample  is  therefore, 

0.8641X8243+0.0405X2250  =  7214  calories 

as  against  7160  calories  with  the  uncorrected  ash  and  7199  calories 
as  actually  determined  in  a  bomb  calorimeter.  The  calculated 
value  with  the  uncorrected  ash  is  39  calories  lower  than  the  value 
determined  in  the  calorimeter  while  the  calculated  value  with 
the  corrected  ash  is  15  calories  higher  or  a  difference  of  24  calories 
in  favor  of  the  result  by  the  corrected  ash. 

As  further  illustration,  samples  of  Ohio  No.  6  coal,  samples 
Nos.  92  and  93  in  Bulletin  No.  9  of  the  Ohio  Geological  Survey 
contain  nearly  the  same  amount  of  ash  but  differ  in  sulphur  by 
1.53  per  cent.  The  moisture,  ash  and  sulphur  and  determined 
calorific  values  are  as  follows: 


Sample  No.  92. 

Sample  No.  93. 

Moisture  
Ash 

5.25 

9  86 

5.90 
10  10 

Sulphur  
Determined  calorific  value 

3.43 
6773 

4.96 
6686 

The  value  obtained  for  H  in  sample  No.  92  is  8220.  The 
calculated  calorific  value  of  Sample  No.  93,  using  this  value  for  H 
and  making  no  corrections  for  the  ash  is  6609.  Assuming  that  the 
difference  in  sulphur  is  due  to  a  difference  in  the  amount  of  pyrite 
present,  and  correcting  the  ash  by  subtracting  f  of  this  sulphur 
difference  and  using  this  corrected  ash,  the  calculated  value  ob- 
tained is  6656.  With  the  uncorrected  ash  the  calculated  value  is 
77  calories  lower  than  the  actually  determined  value.  With  the 
corrected  ash  it  is  only  30  calories  lower  for  this  sample,  a  differ- 
ence of  47  calories  in  favor  of  a  corrected  ash. 

Comparison  of  samples  with  the  same  sulphur  content.  Two 
other  samples  of  Ohio  No.  6  coal,  Samples  Nos.  99  and  104,  in 


42 


COAL 


Bulletin  No.  9  of  the  Ohio  Geological  Survey,  have  essentially 
the  same  sulphur  content  but  differ  in  ash.  The  moisture,  ash, 
sulphur  and  determined  calorific  value  of  the  samples  are  as 
follows : 


Sample  No.  99. 

Sample  No.  104. 

Moisture  

5.44 

5  55 

Ash 

9  28 

5  23 

Sulphur                

3  77 

3  63 

Calorific  value  

6822 

7191 

The  value  obtained  for  H  in  Sample  No.  99  is  8265.  Cal- 
culating the  calorific  value  of  104  from  this  value  for  H  and 
making  no  correction  for  the  ash  gives  7156  as  the  calorific  value. 
Assuming  that  the  difference  in  ash  is  due  to  differences  in  amount 
of  slate  or  clay  in  the  sample,  and  correcting  the  ash  and  calcu- 
lating the  calorific  value  with  corrected  ash,  the  value  obtained 
is  7213  as  against  7191  as  actually  determined  in  a  calorimeter. 
The  uncorrected  ash  result  is  35  calories  too  low,  the  corrected 
ash  is  22  calories  too  high  or  a  difference  of  13  calories  in  favor  of 
the  corrected  ash. 

The  use  of  this  "  corrected  ash  "  should  be  restricted  to  com- 
parisons of  the  ash  in  the  two  samples,  which  is  practically  limit- 
ing it  to  the  ash  difference.  It  cannot  be  used  in  the  formula  for 
obtaining  the  value  for  H,  as  much  of  the  sulphur  present  in  the 
sample  may  be  present  as  organic  sulphur,  also  a  portion  of  the 
ash  is  present  in  other  forms,  as  clay  and  shale.  A  failure  to  cor- 
rect for  the  amounts  of  clay  and  pyrite  means  that  the  actual 
value  for  H  is  too  low  or  too  high.  This  is  however  of  little  im- 
portance as  in  obtaining  the  calculated  calorific  value  of  another 
sample,  approximately  the  same  error  is  present  as  in  the  sample 
from  which  H  is  derived  and  in  the  calculation  one  error  practically 
eliminates  the  other  and  only  the  difference  in  amounts  of  clay 
and  pyrite  need  be  allowed  for.  Since  in  most  samples  of  the  same 
coal  the  difference  in  ash  and  sulphur  is  largely  due  to  differences 
in  amount  of  clay  and  pyrite  present,  this  corrected  formula 
should  in  most  cases  give  somewhat  more  accurate  results. 


CHAPTER   II 

CHEMICAL  ANALYSIS   OF    COAL 
PROXIMATE  ANALYSIS 

THIS  analysis  gives  the  composition  of  the  coal  under  four 
headings  as  follows:  moisture,  volatile  matter,  fixed  carbon, 
and  ash. 

The  results  obtained  are  more  or  less  dependent  upon  the  exact 
process  used  and  small  variations  in  working  out  the  details  of  the 
process  may  make  a  considerable  difference  in  the  results  actually 
obtained,  while  a  distinctly  different  process  gives  radically 
different  values  for  some  of  the  determinations.  Hence  the  re- 
sults are  relative  and  not  absolute  and  should  be  so  regarded  by 
both  the  chemist  and  the  user  of  the  coal.  The  efforts  of  some 
chemists  to  find  a  method  of  determining  the  "  true  moisture  " 
in  coal  might  better  be  spent  in  trying  to  simplify  and  im- 
prove the  method  already  in  use  for  obtaining  the  comparative 
value. 

Moisture.  As  has  already  been  stated,  the  term  moisture 
includes  only  the  more  or  less  loosely  held  water  which  is  driven 
off  by  heating  1  gram  of  the  finely  ground  sample  for  1  hour 
at  105°  C.  A  finely  ground  sample  of  coal  during  the  operation 
undergoes  changes  due  to  oxidation  and  escape  of  gases,  hence 
the  actual  value  obtained  for  moisture  is  the  amount  of  water 
driven  off  plus  or  minus  any  oxidation  changes.  In  most 
coals  if  not  ground  excessively  fine  these  oxidation  changes  are 
of  minor  importance  compared  to  the  moisture  loss  so  that  the 
reporting  of  this  net  loss  as  moisture  does  not  lead  to  any  serious 
errors  although  it  practically  never  represents  the  exact  amount 
of  water  expelled.  A  sample  of  coal  which  has  been  heated  for 
1  hour  at  105°  will  give  off  more  moisture  and  undergo  further 
oxidation  changes  if  heated  to  a  still  higher  temperature,  the 

43 


44  COAL 

amount  of  moisture  given  off  depending  upon  the  kind  of  coal  and 
upon  the  increase  in  temperature.  The  extent  of  the  oxidation 
also  increases  with  the  temperature  and  varies  with  the  kind  of 
coal  and  fineness  of  the  sample.  While  it  is  true  that  the  results 
for  moisture  obtained  by  heating  the  sample  to  105°  have  no 
absolute  value  but  merely  a  relative  one,  it  is  equally  true  when 
two  samples  of  approximately  the  same  kind  of  coal  are  treated 
in  the  same  way  for  moisture  by  heating  to  105°,  the  difference 
in  the  results  obtained  show  very  closely  the  difference  in  the 
amount  of  loosely  held  moisture  in  the  coal.  Usually  this  is  what 
the  user  of  the  coal  wishes  to  know  and  on  this  account  the  mois- 
ture determination  has  importance  and  value. 

Volatile  matter.  The  determination  of  volatile  matter  is  an 
arbitrary  one  and  the  results  are  obtained  by  following  a  certain 
prescribed  procedure,  which  is  essentially  to  heat  1  gram  of  the 
finely  ground  sample  in  a  covered  platinum  crucible  over  the  full 
flame  of  a  Bunsen  burner  for  seven  minutes.  The  loss  in  weight 
represents  moisture  plus  volatile  matter.  Subtracting  the  value 
for  moisture  from  this  result  gives  the  amount  of  volatile  matter 
in  the  coal.  This  determination  cannot  be  regarded  as  entirely 
satisfactory  as  the  result  obtained  is  to  a  considerable  degree 
dependent  upon  the  particular  conditions  under  which  the  sample 
was  run  and  two  different  chemists  in  two  different  laboratories 
both  trying  to  follow  out  the  same  method  of  procedure  may 
easily  obtain  results  for  volatile  matter  upon  the  same  sample  of 
coal  which  may  differ  by  2  or  3  per  cent.  Furthermore,  some  high 
moisture  coals  suffer  mechanical  losses  during  the  heating  to 
drive  off  the  volatile  matter.  Such  samples  require  special  treat- 
ment to  insure  results  of  even  approximate  accuracy.  On 
account  of  such  possible  differences  and  errors  this  determina- 
tion cannot  be  regarded  as  very  exact.  It  is,  however,  true 
that  the  same  chemist  working  in  the  same  way  with  the  same 
crucibles,  the  same  height  of  gas  flame,  the  same  Bunsen  burner, 
etc.,  can  obtain  results  which  will  duplicate  within  a  few  tenths 
of  1  per  cent,  and  in  control  work  the  same  chemist's  results  on 
approximately  the  same  coals  ought  to  be  comparable  among 
themselves  to  within  less  than  1  per  cent.  The  amount  of  vola- 
tile matter  in  itself  gives  very  little  idea  of  the  coal,  as  two  coals 
with  approximately  the  same  amount  of  volatile  matter  may 
differ  very  greatly  in  heating  value,  physical  properties,  etc., 


CHEMICAL  ANALYSIS  OF  COAL  45 

and  any  significance  which  the  determination  of  volatile 
matter  actually  has  is  largely  a  relative  one  which  may  be  of 
value  when  the  same  or  similar  coals  are  compared  with  one 
another. 

The  volatile  matter  consists  essentially  of  any  combined 
water  in  the  coal  plus  a  portion  of  the  sulphur,  on  an  average 
probably  about  one-half  of  the  total  sulphur  present  in  the  coal, 
plus  the  nitrogen  in  the  coal,  plus  hydrocarbons  of  unknown 
and  varying  composition.  The  nitrogen  and  combined  water 
in  the  volatile  matter  have  no  heating  value  and,  if  present 
large  amounts,  the  heating  value  of  the  combustible  will  be 
correspondingly  lower. 

Fixed  carbon.  Fixed  carbon  represents  the  difference  obtained 
by  subtracting  the  percentage  of  moisture,  volatile  matter  and 
ash  from  100.  The  fixed  carbon  as  its  name  indicates  is  mostly 
carbon.  Approximately  one-half  the  sulphur  in  the  coal  present 
in  the  form  of  pyrite  and  a  variable  portion  of  that  present  as 
organic  sulphur  remains  with  the  fixed  carbon  and  the  heating 
value  of  the  fixed  carbon  is,  on  this  account,  somewhat  lower 
than  that  of  pure  carbon.  On  the  other  hand,  small  amounts 
of  hydrogen  may  be  retained  in  the  fixed  carbon  which  would 
slightly  increase  its  heating  value.  In  most  coals  the  heating 
value  per  unit  of  the  fixed  carbon  is  not  far  from  that  of  car- 
bon— 8080 — and  this  value  may  be  used  in  estimating  heat  values 
without  any  great  error.  With  high  sulphur  coals,  a  somewhat 
lower  value,  approximately  30  calories  lower  for  each  per  cent  of 
sulphur  in  the  coal,  is  probably  more  nearly  a  correct  value. 
This  is  based  on  the  assumption  that  one-half  of  the  sulphur 
remains  with  the  fixed  carbon  and  that  not  more  than  traces  of 
hydrogen  are  retained  in  the  fixed  carbon. 

Ash.  As  ordinarily  reported  this  is  the  weight  of  ignited 
mineral  matter  in  the  coal.  The  relation  of  this  ignited 
mineral  matter  to  the  mineral  matter  in  the  coal  has  already 
been  discussed  in  detail  and  no  especial  points  need  repeating 
here. 

Comparison  of  proximate  analyses  of  certain  coals.  As  illus- 
trations of  the  proximate  analyses  of  widely  different  coals  the 
following  determinations  including  sulphur  and  calorific  value 
are  taken  from  Professional  Paper  No.  48  and  Bulletin  No.  290 
of  the  U.  S.  Geological  Survey: 


46 


COAL 


North  D. 
No.  1. 

Wyo. 
No.  1. 

Colorado 
No.  1. 

Mon. 
No.  1. 

Illinois 
No,  4. 

Indiana 
No.  1. 

Ohio 
No.  8. 

Moisture 

35  38 

22  63 

18   68 

11  05 

12  91 

11    40 

7  55 

Volatile  matter. 
Fixed  carbon.  . 
Ash 

29.59 
25.68 
9.35 

35.68 
37.19 
4  50 

34.88 
40.45 
5  99 

35.90 

42.08 
10  97 

31.90 
43.55 
11  64 

33.81 
41.39 
13  40 

38.00 
46.08 
8  37 

Sulphur   

100.00 
1.55 

100.00 
0.59 

100.00 
0.55 

100.00 
1  73 

100.00 
1  32 

100.00 
2  50 

100.00 

2  84 

Calories 

3846 

5408 

5635 

5855 

6002 

6145 

6738 

(N 

o 

(N 

6 

<N 

55 

rH* 

r~l 

6 

»0 

0 

6 

C 

>> 

6 

^6 

^ 

6 

55 

55 

55 

0 

55 

<< 

2 

55 

rt 

2 

03 

>j 

S 

03 

'5 

'3 

1 

fc 

I 

o 

'£? 

S 

"S 

'S 

1 

H 

03 

3 

a 

> 

1 

c 

0) 

**^ 

c3 

< 

0) 

<jj 

OT 

S 

-9 
a 

^ 

^ 

OJ 

Moisture  

3.36 

4.45 

2.34 

3.10 

1.75 

2.36 

1.75 

1.72 

Volatile  matter.  . 

32.88 

36.15 

31.84 

36.12 

36.77 

12.68 

18.59 

17.85 

Fixed  carbon  .  .  . 

51.33 

48.40 

53.28 

56  .  39 

55.14 

72.88 

75.08 

73.56 

Ash  

12.43 

11.00 

12.54 

4.39 

6.34 

12.08 

4.58 

6.87 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

Sulphur  

1.01 

1  .  52 

0.72 

1.22 

0.90 

1.99 

0.56 

0.68 

Calories  

6861 

7004 

7142 

7860 

7837 

7366 

8346 

8095 

This  series  of  samples  was  selected  not  as  representing  the 
coals  of  these  regions  but  to  show  the  wide  variation  in  moisture 
and  volatile  matter  and  fixed  carbon  in  different  coals  and  the 
variable  heating  value  of  the  volatile  matter.  The  variable 
heating  value  of  the  volatile  matter  can  be  most  strikingly 
seen  by  comparing  the  different  values  for  H  in  these  differ- 
ent coals.  H,  as  has  already  been  explained,  is  the  heating 
value  per  unit  of  "  residual  coal  "  and  is  obtained  by  dividing 
the  total  calorific  value  less  the  calorific  value  of  the  sulphur 
present  by  one  minus  the  sum  of  the  moisture,  ash  and  sul- 
phur. The  values  for  H  for  the  different  samples  are  as 
follows: 


CHEMICAL  ANALYSIS  OF  COAL 


47 


VALUE  FOR  // 


Calorics. 

Nitrogen, 
Per  Cent. 

North  Dakota,  No.  1  

7094 

0.54 

Wyoming  No   1              .                      .... 

7464 

1  02 

Colorado,  No.  1  

7519 

1.15 

JMontana  No   1 

7627 

1  33 

Illinois,  No.  4      

8056 

1  15 

Indiana  No   1 

8375 

1  18 

Ohio,  No.  8                   

8216 

1  29 

Alabama  No  2 

8219 

1  54 

Indian  Territory,  No.  2    

8395 

1  67 

Alabama,  No.  1  

8443 

65 

Kentucky,  No.  1 

8580 

83 

West  Virginia,  No.  1  

8589 

54 

Arkansas,  No   5 

8760 

37 

West  Virginia,  No.  10  
West  Virginia,  No.  12  

8950 
8905 

.06 
33 

The  value  ranges  from  about  7100  to  over  8900,  an  extreme 
difference  of  nearly  1900  calories.  As  the  moisture  and  ash  in 
the  samples  have  no  heating  value  and  the  value  of  the  fixed 
carbon  is  approximately  the  same  per  unit  of  fixed  carbon  in  all 
the  samples^the  great  difference  in  the  value  of  H  is  due  to  the 
variable  composition  of  .this  volatile  matter.  The  inert  con- 
stituents of  the  volatile  matter  are  nitrogen  and  combined  water. 
The  amount  of  nitrogen  in  the  different  samples  is  given  in 
the  foregoing  table. 

The  extreme  difference  is  less  than  1J  per  cent  and  the  effect 
of  nitrogen  on  the  value  for  H  is  of  minor  importance. 

As  has  been  mentioned  in  connection  with  Dulong's  formula 
and  its  modifications,  a  greater  part  but  not  all  of  the  oxygen  in 
the  coal  appears  in  the  form  of  water.  The  exact  relation  between 
the  small  amount  properly  belonging  with  carbon  and  that 
present  as  water  varies  with  each  coal,  but  for  purposes  of  com- 
parison all  of  it  can  be  assumed  as  present  as  water  without 
serious  error,  bearing  in  mind  however,  that  the  values  for 
combined  water  on  this  assumption  are  all  somewhat  high.  On 
this  assumption  the  combined  water  in  the  samples  is  as 
follows : 


48 


COAL 


Oxygen. 

Total 
Water. 

Moisture. 

Combined 
Water. 

North  Dakota,  No.  1 

41  72 

46  93 

35  38 

11  55 

Wyoming,  No.  1  

32  59 

36  66 

22  63 

14  03 

Colorado,  No.  1 

28  78 

32  38 

18  68 

13  70 

Montana,  No.  1  

21  52 

24  21 

11  05 

13  16 

Illinois  No  4 

19  72 

22  18 

12  91 

9  27 

Indiana,  No.  1  
Ohio  No  8 

17.21 
15  00 

19.36 
16  87 

11.40 

7  55 

7.96 
9  32 

Alabama,  No.  2     

11  49 

12  93 

3  36 

9  57 

Indian  Territory,  No.  2  

11  15 

12  54 

4  45 

8  09 

Alabama  No   1 

8  50 

9  56 

2  34 

7  22 

Kentucky,  No.  1    

9  76 

10  98 

3  10 

7  88 

West  Virginia,  No.  1  

7  94 

8  93 

1  75 

7  18 

Arkansas,  No.  5 

4  30 

4  84 

2  36 

2  48 

West  Virginia,  No.  10  

4  18 

4  70 

1  75 

2  95 

West  Virginia,  No.  12 

3  98 

4  48 

1  72 

2  76 

An  inspection  of  the  values  for  combined  water  shows  a 
variation  of  from  14  per  cent  in  the  highest  to  2J  per  cent  in 
the  lowest,  or  a  variation  of  about  12  per  cent.  The  highest 
combined  water  however  is  not  found  in  the  sample  having  the 
lowest  value  for  H  so  that  the  variable  composition  of  the  volatile 
hydrocarbons  must  be  compared  in  order  to  more  completely 
explain  the  variation  in  H .  The  total  hydrogen  in  these  samples 
as  shown  by  the  ultimate  analysis  and  the  available  hydrogen 
which  is  the  amount  left  after  subtracting  that  as  combined 
water  are  as  follows: 


Total 
Hydrogen. 

Available 
Hydrogen. 

North  Dakota  No   1 

6  61 

1  40 

Wyoming  No   1               .... 

6  39 

2  32 

Colorado,  No.  1  

6  07 

2  47 

IVtontana   No   1 

5  37 

2  68 

Illinois  No  4                

5  43 

2  97 

Indiana,  No.  1  

5  37 

3  22 

Ohio  No  8 

5  48 

3  60 

Alabama  No  2                 

4  84 

3  40 

Indian  Territory  No  2 

5  17 

3  78 

Alabama  No   1 

5  01 

3  95 

Kentucky   No.  1        

5  43 

4  21 

\Vest  Virginia  No   1 

5  28 

4  29 

Arkansas   No  5                         

3  82 

3  28 

West  Virginia,  No.  10  

4  65 

4  13 

West  Virginia  No   12 

4  43 

3  93 

CHEMICAL  ANALYSIS  OF  COAL 


49 


Listing  the  volatile  constituents  under  the  following  head- 
ings: combined  water,  nitrogen,  sulphur,  available  hydrogen 
and  carbon,  the  following  values  are  obtained  for  the  different 
samples: 


Total 
Volatile. 

Com- 
bined 
Water. 

Nitrogen. 

Sulphur. 

Avail- 
able 
Hydro- 
gen. 

Carbon. 

North  Dakota,  No.  1  
Wyoming,  No.  1 

29.59 
35  58 

11.55 
14  03 

0.54 
1  02 

0.78 
0.30 

1.40 
2  32 

15.32 
17  91 

Colorado,  No  1  

Montana,  No.  1 

34.88 
35  90 

13.70 
13  16 

1.15 
1  33 

0.28 
0  86 

2.47 
2  68 

17.28 
17  87 

Illinois,  No.  4  
Indiana,  No.  1  

31.90 
33.81 

9.27 
7.96 

1.15 
1.18 

0.66 
1.25 

2.97 
3.22 

17.85 
20.20 

Ohio  No.  8 

38  00 

9  32 

1  29 

1  90 

3  60 

21.89 

Alabama,  No.  2  
Indian  Territory,  No.  2  .  . 
Alabama,  No.  1 

32.88 
36.15 
31.84 

9.57 
8.09 

7  22 

1.54 
1.67 
1  65 

0.50 
0.51 
0  36 

3.40 
3.78 
3.95 

17.87 
22.10 
18.66 

Kentucky,  No.  1  

36.12 

7.88 

1.83 

0.72 

4.21 

21.48 

West  Virginia,  No.  1  
Arkansas,  No.  5  
West  Virginia,  No.  10  
West  Virginia,  No.  12.  ... 

36.77 
12.68 
18.59 
17.85 

7.18 
2.48 
2.95 
2.76 

1.54 
1.37 
1.06 
1.33 

0.30 
1.00 
0.19 
0.28 

4.29 
3.28 
4.13 
3.93 

23.46 
4.55 
10.26 
9.55 

The  amount  of  sulphur  in  the  volatile  matter  varies  with  the 
nature  of  the  occurrence  of  the  sulphur  from  as  low  as  f 
to  as  high  as  f  of  the  total  sulphur  present.  On  the  follow- 
ing samples  the  amount  of  sulphur  in  the  volatile  matter 
is  calculated  from  the  results  on  the  coke  tests  given  in 
Professional  Paper  No.  48  and  in  Bulletin  No.  290  of  the 
U.  S.  Geological  Survey.  The  approximate  percentages  of  the 
total  sulphur  in  the  coke  and  in  the  volatile  matter  are  as 
follows : 


Coke. 

Volatile  Matter. 

Indian  Territory  No  2 

Per  Cent. 

67 

Per  Cent. 
33 

Kentucky,  No.  1 

40 

60 

Ohio,  No.  8    ...            ...                   

33 

67 

West  Virginia,  No.  1  
West  Virginia,  No.  10 

67 
67 

33 
33 

West  Virginia,  No.  12  

60 

40 

50  COAL 

On  the  remaining  samples  on  which  no  coke  tests  were 
made,  the  amount  of  sulphur  in  the  volatile  matter  is  esti- 
mated as  50  per  cent  of  the  total  amount  present.  This  is  of 
course  an  assumption  but  the  error  introduced  by  it  can  in  ho 
case  be  very  large,  not  large  enough  to  materially  change  the 
final  findings  as  to  the  nature  and  heating  value  of  the  volatile 
matter. 

The  carbon  values  are  obtained  by  subtracting  the  sum  of 
the  combined  water  plus  the  nitrogen  plus  the  sulphur  plus  the 
available  hydrogen  from  the  total  volatile  matter.  The  heat 
per  unit  of  volatile  matter  may  be  calculated  by  Dulong's 
formula  and  is  equal  to: 

(8080 XCarbon)  +  (34460 X available  Hydrogen)  +  (2250 XSulphur) 

Volatile  matter 

The  results  for  each  of  the  samples  are  as  follows: 

North  Dakota,  No.  1 5874 

Wyoming,  No.  1 6332 

Colorado,  No.  1 6459 

Montana,  No.  1 6649 

Illinois,  No.  4 7774 

Indiana,  No.  1 , 8193 

Ohio,  No.  8     8034 

Alabama,  No.  2 7989 

Indian  Territory,  No.  2 8575 

Alabama,  No.  1 9036 

Kentucky,  No.  1 8868 

West  Virginia,  No.  1 9195 

Arkansas,  No.  5 11995 

West  Virginia,  No.  10 12135 

WTest  Virginia,  No.  12 11944 

These  results  show  a  range  for  the  heating  value  of  the  volatile 
matter  of  from  about  5900  to  over  12,000  calories  or  a  difference 
of  over  100  per  cent  in  heating  value  per  unit  of  volatile  matter. 
The  highest  heating  value  is  found  in  those  coals  which  are  rela- 
tively high  in  available  hydrogen,  and  at  the  same  time  are  low 
in  combined  water.  West  Virginia  No.  10  with  a  value  of  8950 
for  H  has  over  4  per  cent  of  available  hydrogen  and  less  than  3 
per  cent  of  combined  water,  while  North  Dakota  No.  1  has  only 
1.4  per  cent  available  hydrogen  and  11.55  per  cent  of  combined 


CHEMICAL   ANALYSIS  OF  COAL  51 

water.  These  values  make  clear  that  in  order  to  determine 
anything  very  definite  about  the  actual  heating  value  of  the  coal, 
something  more  than  the  proximate  analysis  is  required.  The 
value  of  this  determination  is  merely  a  relative  one  and  should 
be  restricted  to  a  comparison  of  different  samples  of  the  same 
bed,  or  at  most  to  different  coals  known  to  be  somewhat  similar 
in  the  relative  amounts  of  oxygen  and  available  hydrogen  which 
are  contained  in  a  unit  amount  of  the  "  residual  coal."  This 
term  "  residual  coal/'  from  what  has  been  given  above,  is  less 
misleading  than  the  more  commonly  used  term  "  combustible," 
since  in  many  of  the  samples  a  large  part  of  the  volatile  matter 
is  non-combustible. 

ULTIMATE  ANALYSIS 

This  analysis  gives  the  composition  of  the  coal  under  the 
following  headings:  percentages  of  carbon,  hydrogen,  nitrogen, 
sulphur,  oxygen  and  ash.  The  percentage  of  oxygen  is  ob- 
tained by  subtracting  the  sum  of  the  other  percentages  from 
100.  Hence  the  algebraic  sum  of  all  the  errors  in  the  other 
determinations  appears  in  the  value  obtained  for  oxygen  which 
makes  the  accuracy  of  the  obtained  value  for  oxygen  somewhat 
uncertain.  Corrections  in  the  ash  may  improve  the  oxygen  value 
somewhat,  but  as  has  been  discussed  under  "  Ash  "  this  correc- 
tion is  not  entirely  satisfactory.  As  the  errors  in  the  oxygen  are 
dependent  upon  the  errors  in  the  other  determinations  the  approx- 
imate limits  of  the  accuracy  of  these  determinations  must  be 
considered  in  order  to  obtain  an  idea  of  the  probable  accuracy 
of  the  oxygen  determination. 

The  determination  of  the  carbon  and  hydrogen  requires  a 
high  degree  of  skill  and  care  in  order  to  secure  satisfactory  results. 
The  results  of  determinations  made  by  poor  manipulators  or 
under  unfavorable  conditions  may  easily  be  1  or  2  per  cent  in 
error  for  carbon  and  0.4  or  0.5  of  1  per  cent  in  error  for  hydrogen. 
With  careful  manipulation  and  proper  conditions  the  carbon  and 
hydrogen  results  in  most  samples  should  be  accurate  to  within  0.2 
of  1  per  cent  for  carbon  and  within  about  0.05  or  0.06  of  1  per  cent 
for  hydrogen,  provided  that  the  laboratory  sample  of  coal  has  been 
previously  reduced  to  approximately  an  air  dry  condition.  Unless 
the  latter  has  been  done,  the  errors  incident  to  weighing  out  small 


52  COAL 

amounts  of  sample  for  ultimate  analysis  makes  a  high  degree  of 
accuracy  practically  impossible.  The  question  of  air  drying  of 
the  samples  is  discussed  in  detail  under  the  head  of  "  Sampling." 
The  results  for  sulphur,  nitrogen  and  ash  should  be  accurate 
within  0.05  of  1  per  cent  and  the  value  obtained  for  oxygen 
can  be  duplicated  to  within  0.25  of  1  per  cent  on  coals  which  are 
fairly  low  in  oxygen.  Whether  it  is  within  0.25  of  1  per  cent 
for  the  oxygen  as  it  actually  occurs  in  the  sample  is  not  so  cer- 
tain, since  in  high  ash  coals  the  possible  corrections  to  the  ash 
are  several  times  this  amount.  The  actual  value  obtained  for 
oxygen  for  small  differences  has  a  relative  value  rather  than  an 
absolute  one.  Large  differences,  such  as  are  shown  in  the  list  of 
samples  given,  have  an  absolute  value  in  indicating  the  nature  of 
the  coal,  the  errors  in  the  determination  or  corrections  for  the  ash 
being  of  minor  importance  compared  to  the  total  difference  in  the 
oxygen  value. 

While  the  results  for  the  ultimate  analysis  should  be  accurate 
to  within  about  the  limits  given  for  the  sample  as  analyzed,  it 
does  not  necessarily  follow  that  these  results  actually  come  this 
near  to  representing  the  original  coal,  as  this  is  dependent  upon 
whether  the  sample  itself  is  representative  of  the  coal.  This  is 
another  question  in  itself  and  is  discussed  in  detail  under  the  head 
of  "  Sampling." 

The  complete  ultimate  analyses  and  the  determined  and 
calculated  heating  values  expressed  in  calories  and  British  ther- 
mal units  on  the  different  coals,  the  proximate  analyses  of  which 
have  already  been  given  are  given  on  page  53,  the  calculated 
values  being  based  on  Dulong's  formula: 

8080C+34460(H  -  JO)  +2250S. 

Some  of  the  variations  in  the  results  are  as  follows:  total 
hydrogen  3.82  to  6.61;  carbon  40.23  to  84.97;  oxygen  3.98  to 
41.72,  and  nitrogen  0.54  to  1.83.  Such  wide  variations  in  the 
ultimate  composition  make  it  easy  to  understand  why  the  heating 
values  likewise  have  such  a  wide  range,  from  3767  to  8346  calories, 
and  help  to  make  more  clear  the  statement  that  "coal  as  it 
actually  occurs  in  nature  differs  widely  in  physical  and  chemical 
properties." 


CHEMICAL  ANALYSIS  OF  COAL 


53 


fO 

03 
O 

03 

Q 

J3 

6 

M 

a 

a 

o 

£ 

Colorado  No.  1. 

Montana  No.  1. 

^6 

'o 

Indiana  No.  1. 

GO 

6 

0 
M 

O 

Alabama  No.  2. 

Hydrogen  

6.61 
40.23 
0.54 
41.72 
1.55 
9.35 

6.39 
54.91 
1.02 
32.59 
0.59 
4.50 

6.07 
57.46 
1.15 
28.78 
0.55 
5.99 

5.37 
59.08 
1.33 
21.52 
1.73 
10.97 

5.43 
60.74 
1.15 
19.72 
1.32 
11.64 

5.37 
60.34 
1.18 
17.21 
2.50 
13.40 

5.48 
67.02 
1.29 
15.00 

2.84 
8.37 

4.84 
68.69 
1.54 
11.49 
1.01 
12.43 

Carbon 

Nitrogen  

Oxygen  
Sulphur  

Ash 

Calories  
B.t.u  

100.00 

3846 
6923 

3767 
6781 

100.00 

5408 
9734 

5247 
9445 

100.00 
Heatir 

5635 
10143 

Heat 

5508 
9913 

100.00 
ig  value 

5855 
10539 

ng  vak 

5739 
10330 

100.00 
5  detern 

6002 
10804 

ic  calcu 

5959 
10726 

100.00 
lined  : 

6145 
11061 

lated: 

6044 
10880 

100.00 

6738 
12128 

6718 
12092 

100.00 

6861 
12350 

6745 
12140 

Calories  
B.t.u  

6 

^ 

rH> 

1-1 

ft 

10 

!«• 

6 

0 

03 

'3 

6 
ft 

03 

'3 

'Sbo 

03 

'3 

E-"  6 

03 

3 

03 

o 

1 

i 
1 

£d 

'•3 

| 

g 

o 

m*2* 

!^ 

a    • 

< 

M 

^ 

.3 

^ 

£ 

Hydrogen  

5.17 

5.01 

5  .43 

5.28 

3.82 

4.65 

4.43 

Carbon    . 

69  49 

71  58 

77.37 

78.00 

76.44 

84  97 

82  71 

Nitrogen  

1  67 

1.65 

1.83 

1.54 

1.37 

1.06 

1  33 

Oxvffen 

11  15 

8  50 

9  76 

7.94 

4  30 

4  18 

3  98 

Sulphur  

1.52 

0.72 

1.22 

0.90 

1.99 

0.56 

0.68 

Ash 

11  00 

12  54 

4  39 

6  34 

12  08 

4  58 

6  87 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

Heating  value  determined: 

Calorics  

7004  |     7142 

7860 

7837 

7366 

8346 

8095 

B.t  u. 

19G07      12856 

141  AS 

1/1107 

1  2950 

15023 

14751 

Heating  value  calculated: 

Calorics     .  .  . 

6952 

7160 

7729 

7801 

7353 

8299 

8054 

B.t.u.   

12514 

12888 

13912 

14042 

13235 

14938 

14498 

54  COAL 

Calculating  an  ultimate  analysis.  From  what  has  been 
stated  concerning  the  difficulties  in  the  carbon  and  hydrogen 
determinations,  it  may  rightfully  be  inferred  that  the  ultimate 
analysis  is  a  somewhat  troublesome  and  expensive  determination 
and  for  most  purposes  where  an  ultimate  analysis  is  required, 
as  in  a  boiler-test  heat  balance,  a  calculated  ultimate  analysis, 
based  on  an  actual  ultimate  analysis  of  a  similar  sample  of  the 
same  coal,  is  fairly  satisfactory.  If  the  percentage  of  moisture, 
ash  and  sulphur  in  each  sample  be  subtracted  from  100  the 
remainder  is  the  per  cent  of  residual  coal  in  each  sample  and  the 
calculation  of  the  derived  ultimate,  based  on  the  assumption  that 
the  residual  coal  in  each  sample  has  approximately  the  same 
percentage  composition,  is  as  follows:  The  determined  ultimate 
analysis  is  given  in  per  cent  of  carbon,  hydrogen,  nitrogen,  oxygen, 
sulphur  and  ash  per  unit  of  coal.  Representing  these  percentages 
by  C,  H,  N,  O,  S,  and  A  and  the  percentages  of  the  derived  samples 
by  C',  H',  N',  0',  S',  and  A'  and  the  moisture,  ash  and  sulphur 
in  the  two  samples  by  M,  A,  and  S  and  M',  A',  and  S'  respect- 
ively, then  the  procedure  is  as  follows: 

Subtract  the  hydrogen,  H,  and  oxygen,  0,  corresponding  to  the 
moisture,  M,  from  the  total  hydrogen  and  oxygen  as  given  in 
the  ultimate  analysis.  The  remainder  will  be  the  hydrogen  and 
oxygen  in  the  residual  coal.  Represent  the  residual  coal  (100  — 
(M+A-f  S),in  the  sample  by  R  and  the  residual  coal  (100-(M'+ 
A'+S'),  in  the  sample  to  be  calculated  by  R'.  The  carbon, 
hydrogen,  oxygen,  and  nitrogen  in  a  unit  of  residual  coal  = 

fc 
O-SM   livi(lcdb  R- 

N 

Multiplying  these  values  by  R'  gives  the  amount  of  carbon, 
hydrogen,  oxygen  and  nitrogen  in  the  residual  coal,  R'.  .  To 
get  the  ultimate  composition  of  the  coal  corresponding  to  R',  the 
hydrogen  and  oxygen  must  be  corrected  by  adding  to  these 
obtained  values  the  correction  corresponding  to  the  moisture,  M'. 
For  hydrogen  this  correction  =  iM',  for  oxygen  fM'. 

IQO-CM'+A'+S')        R' 

If  -  or  — -  be  represented  by  K  the  ultimate 

100— (M+A+S)          R 

analysis  of  the  derived  sample  is  as  follows: 


CHEMICAL  ANALYSIS  OF  COAL 


55 


'  =  (H-iM)K+iM' 
'  =  (O-9M)K+|M' 


A'  =  A' 


Total 


100 


The  agreement  between  the  calculated  and  determined  ulti- 
mates  is  shown  by  determinations  on  samples  Nos.  1061  and 
and  1157,  Professional  Paper,  No.  48,  U.  S.  Geological  Survey, 
the  moisture,  ash  and  sulphur  in  which  are  as  follows: 


Sample  No.  1157. 

Sample  No.  1061. 

Moisture                     

2.56 

2  03 

Ash               

13.92 

13.46 

Sulphur 

0  78 

5  39 

Sample  No.  1157  is  a  portion  of  Alabama  No.  1  and  Sample  No. 
1061  is  a  portion  of  Kansas  No.  3  coal.  The  determined  and 
calculated  values  for  carbon  and  hydrogen  on  these  two  samples 
are  as  follows: 


Sample  No. 

Determined 
Hydrogen. 

Calculated 
Hydrogen. 

Determined 
Carbon. 

Calculated 
Carbon. 

1157 

4.82 

4.94 

70.00 

70.19 

1061 

4.77 

4.84 

68.94 

68.85 

The  proximate  and  ultimate  analysis  of  the  car  samples  from 
which  the  ultimates  are  derived  are  given  in  the  analytical  tables 
in  Chapter  X. 

The  derived  results  for  carbon  differ  from  the  actually  deter- 
mined results  by  an  amount  within  the  limit  of  variation  of 
duplicate  determinations  of  carbon.  The  variations  between  the 
determined  and  derived  hydrogen — 0.07  and  0.12 — are  not  much 
greater  than  the  errors  in  the  actual  hydrogen  determinations  and 
a  calculated  ultimate  based  on  a  carefully  run  ultimate  of  a  similar 


56  COAL 

sample  of  coal  is  in  the  opinion  of  the  author  likely  to  be  as  reli- 
able as  an  actual  determination  made  by  an  average  manipu- 
lator under  ordinary  working  conditions.  Certainly  the  error 
introduced  is  usually  not  large  enough  to  have  any  great  effect 
upon  the  calculations  which  are  affected  by  it. 

Effect  of  errors  in  the  ultimate  analysis  on  the  heat  balance. 
For  illustration,  assume  a  maximum  error  of  1  per  cent  in  the  cal- 
culated value  for  carbon  and  0.2  per  cent  in  the  calculated  value 
for  hydrogen.  Then  0.01  gram  of  carbon  is  equivalent  to  0.0367 
gram  of  CO2-  The  nitrogen  equivalent  to  the  oxygen  from  the 
air  required  to  produce  this  amount  of  CO2  =  0.10  gram;  allowing 
100  per  cent  excess  air  =  0.128  gram  of  air.  On  the  boiler  test 
with  the  products  of  combustion  escaping  at  300°  C.  (572°  F.) 
the  sensible  hea't  carried  off  in  these  products  is  about  19  calories. 
0.2  per  cent  of  hydrogen  =  0.018  gram  of  H^O.  The  latent  heat 
of  this  amount  of  water  equals  10.6  calories.  The  sensible  heat, 
assuming  the  gases  escaping  at  300°  C.,  in  this  amount  of  water 
is  2.7  calories.  The  nitrogen  equivalent  to  the  oxygen  required  to 
combine  with  this  amount  of  hydrogen  equals  0.053  gram.  Allow- 
ing 100  per  cent  excess  air,  the  amount  of  air  required  for  the 
excess  is  0.069  gram.  The  sensible  heat  carried  off  at  300°  C.  by 
this  amount  of  air  and  nitrogen  equals  about  8  calories,  making 
the  total  heat  carried  off  about  21  calories.  If  the  errors  in  carbon 
and  hydrogen  are  both  high  or  both  low  at  the  same  time,  the 
total  error  in  the  distribution  of  the  heat  loss  amounts  to  about 
40  calories  or  about  ^  per  cent  of  the  total  heat  produced;  as 
the  radiation  and  unaccounted-for  losses  in  a  boiler  test  are  fre- 
quently 20  times  this  large,  it  is  apparent  that  the  error  from  the 
use  of  a  calculated  ultimate  of  approximate  accuracy  has  little 
effect  upon  the  actual  results  of  the  boiler  test. 


CHAPTER   III 
SAMPLING 

THE  old  saying  that  a  chain  is  only  as  strong  as  its  weakest 
link  may  well  be  applied  to  the  valuation  of  the  results  of  chemical 
tests  and  many  times  the  weakest  link  is  the  sampling.  This  may 
be  due  to  one  or  more  of  several  reasons: 

(1)  Failure   to   secure   a   representative   sample   due   to  the 
faulty  method  of  sampling,  as  for  example  the  sampling  of  a  car 
of  coal  by  merely  taking  several  lumps  or  shovel  fulls  from  the 
top  of  the  car. 

(2)  Difficulty  in  securing  a  representative  sample  due  to  the 
occurrence  and  the  irregular  distribution  of  materials  of  different 
composition,  as  the  irregular  distribution  of  pyrite  in  coal  or  the 
irregular  distribution  of  gold  in  gold  ores. 

(3)  Alterations  or  changes  in  the  sample  during  handling  or 
before  it  is  analyzed,  as  changes  due  to  gain  or  loss  of  moisture  or 
changes  due  to  oxidation. 

Failure  to  secure  a  representative  sample  due  to  any  or  all  of 
these  causes  may  result  in  errors  ten  times  as  large  as  any  of  the 
probable  chemical  errors  and  too  much  emphasis  cannot  be  laid 
on  the  importance  of  care  and  thoroughness  in  taking  and  hand- 
ling the  sample  on  which  the  chemical  results  are  to  be  obtained. 
If  necessary  as  much  or  more  time  and  money  should  be  expended 
in  securing  a  sample  as  is  expended  in  having  it  analyzed,  as  the 
determinations  of  the  chemist  if  properly  made  represent  only  the 
sample  as  received  and  if  made  on  improperly  taken  samples 
they  may  be  so  far  from  representing  the  actual  material  as  to  be 
worse  than  useless.  The  practice  of  entrusting  sampling  to 
ignorant  laborers  or  mere  boys  having  little  or  no  idea  of  what 
they  are  doing  deserves  to  be  strongly  condemned,  as  skill  and 
training  are  as  essential  in  taking  and  handling  a  sample  as  in  mak- 
ing the  chemical  determinations.  It  is  indeed  true  that  an  ordin- 
ary laborer  can  be  trained  to  the  work  and  can  take  the  samples 

57 


58  COAL 

properly  but  the  training  should  be  thorough  as  to  details  and 
strict  observance  of  details  insisted  upon  if  the  results  are  to  be 
of  value  and  too  often  the  persons  giving  instructions  in  sampling 
do  not  themselves  appreciate  the  importance  of  some  of  the  neces- 
sary precautions. 

In  sampling  coal  the  effect  upon  the  sample  of  the  three  vari- 
able factors,  moisture,  ash  and  sulphur,  should  be  considered 
separately  and  collectively.  The  amounts  of  these  constituents 
vary  in  the  different  materials  composing  the  coal  (i.e.,  in  the 
coal,  slate,  pyrite,  etc.)  and  also  in  different  parts  of  these 
separate  constituents,  as  in  the  lump  and  fine  coal.  Hence  to 
secure  a  representative  sample,  it  is  essential  that  the  amount 
of  lump  coal,  fine  coal,  slate,  clay  and  pyrite  in  the  sample  be 
proportionate  to  that  in  the  entire  lot  of  coal  sampled.  The  prob- 
lem of  the  sampler  therefore  is  to  endeavor  to  get  this  propor- 
tionate amount  for  each  of  the  samples  taken. 

The  details  of  handling  and  taking  the  sample  are  dependent 
upon  what  it  is  desired  that  the  sample  shall  represent.  For 
example,  when  sampling  coal  in  the  mine  what  the  operator 
often  desires  especially  to  find  out  are  the  variations  in  ash  and 
sulphur  in  order  that  the  average  ash  and  sulphur  of  the  coal 
shipped  from  the  different  parts  of  the  mine  may  be  estimated. 

The  moisture  variations  in  the  samples  in  this  particular  case 
are  of  minor  importance  and  the  moisture  content  in  such  mine 
samples  when  analyzed  may  differ  by  several  per  cent  from  the 
amount  of  moisture  that  the  coal  actually  contains  in  the  mine. 
However,  this  difference  has  very  little  effect  upon  the  percent- 
ages obtained  for  ash  and  sulphur.  For  illustration,  suppose 
that  the  sample  taken  in  the  mine  analyzed  as  follows:  Mois- 
ture 5  per  cent,  ash  7  per  cent  and  sulphur  2  per  cent  and  that 
the  true  moisture  content  of  the  coal  in  the  mine  is  10  per  cent. 
Then  the  analysis  of  this  sample  reduced  to  mine  conditions  is 
moisture  10  per  cent,  ash  6.75  per  cent  and  sulphur  1.90  per  cent. 
The  effect  of  variation  in'  moisture  on  the  ash  percentage  is  as  a 
rule  of  minor  importance  to  the  operator.  On  the  other  hand,  if 
the  sample  is  to  represent  the  coal  as  fired  under  a  boiler  any  failure 
to  secure  the  proper  result  in  moisture  is  simply  an  error  propor- 
tionate to  the  amount  of  moisture  gain  or  loss.  In  the  illustration 
just  given  the  5  per  cent  difference  in  moisture  means  a  5  per 
cent  difference  in  the  heating  value  of  the  coal  and  approximately 


SAMPLING  59 

a  5  per  cent  difference  in  the  value  of  the  coal  in  dollars  and 
cents. 

The  sampling  of  coal  may  be  considered  under  two  general 
heads:  Sampling  of  coal  as  it  occurs  in  the  mine  and  sampling 
of  lots  of  coal  as  bought  and  sold  or  as  used. 

Sampling  coal  in  the  mine.  In  sampling  coal  in  the  mine  a 
number  of  factors  are  to  be  considered,  as  the  number  of  samples 
to  be  taken,  their  location  and  the  method  of  taking  them.  For 
a  mine  shipping  coal  the  directions  of  the  Bureau  of  Mines  specify 
not  less  than  4  samples  for  a  daily  production  of  200  tons  or  less, 
with  an  additional  sample  for  each  additional  200  tons  of  coal 
mined  per  day.  The  number  should  be  greater  from  mines  in 
which  the  quality  of  the  coal  varies  greatly.  The  location  of  the 
samples  taken  should  be  such  as  to  fairly  represent  the  coal  being 
worked.  Other  samples  in  head  entries  or  in  the  deepest  portions 
of  the  mine  may  be  taken  if  desired  in  order  to  indicate  the  char- 
acter of  the  future  output. 

In  selecting  the  exact  place  to  take  a  sample,  care  should  be 
taken  to  avoid  exceptional  features,  such  as  faults  or  irregular 
patches  or  partings  or  veins  of  pyrite.  A  freshly  exposed  face  of 
the  coal  should  be  selected  and  before  taking  the  sample  the  face 
should  be  freed  or  cleaned  from  any  dirt  or  loose  coal  from  roof 
to  floor  for  a  width  of  5  or  6  feet.  This  is  done  in  order  to  pre- 
vent fragments  of  foreign  matter  from  falling  off  the  face  and 
becoming  mixed  with  the  sample.  For  the  same  reason,  insecure 
portions  of  the  roof  should  also  be  carefully  taken  down.  The 
face,  where  the  sample  is  to  be  cut,  should  be  squared  up  and  an 
inch  or  so  of  the  surface  cut  away  with  the  pick  before  actually 
cutting  the  channel  sample.  In  cutting  the  sample  a  uniform 
cut  should  be  made  across  the  face  of  the  seam  including  in  the 
sample  all  that  portion  that  is  included  in  the  coal  as  mined  and 
rejecting  any  portions  which  would  be  rejected  in  good  mining 
practice.  The  amount  of  coal  taken  for  a  sample  should  be 
sufficient  to  reasonably  insure  a  fair  representation.  The  sample 
obtained  from  a  channel  1  inch  wide  and  1  inch  deep  if  strictly 
uniform  in  width  and  depth  is  satisfactory  but  no  sampler  can 
cut  such  a  channel  and  a  channel  4  to  8  inches  wide  by  2  to  4 
inches  deep  should  be  cut,  the  errors  in  width  and  depth  being 
relatively  much  less  with  a  wide  and  deep  cut  than  with  a  narrow 
and  shallow  one. 


60  COAL 

In  collecting  the  sample  a  large  canvas  or  oil  cloth  about  7 
ft.  square  should  be  spread  on  the  floor,  care  being  taken  that 
mud  and  dirt  are  not  introduced  into  the  sample  from  the  boots 
or  shoes  of  the  sampler.  With  a  uniform  depth  and  width  of  cut 
the  amount  of  the  sample  cut  varies  with  the  height  of  the  seam. 
The  directions  of  the  United  States  Government  for  sampling 
are  to  take  at  least  6  pounds  for  each  foot  of  thickness.  This 
amount  corresponds  approximately  to  a  channel  2x6  or  3x4  inches. 
After  cutting  the  sample  it  should  be  either  shipped  entire  or  if 
a  sampling  outfit  is  available  it  may  be  broken  down  till  the 
coarsest  particles  pass  through  a  f-inch  screen,  especial  care  being 
taken  to  crush  all  lumps  of  slate  and  pyrite  quite  fine.  The 
sample  may  then  be  reduced  after  thorough  mixing  by  quarter- 
ing and  rejecting  the  opposite  quarters,  taking  care  to  brush  away 
the  entire  part  of  the  rejected  portions.  The  two  remaining 
quarters  may  be  again  mixed  and  quartered  until  the  final  prod- 
uct amounts  to  not  less  than  8  or  10  pounds.  If  a  f-inch  sieve 
is  available  this  10-pound  portion  may  be  crushed  until  the 
largest  particles  pass  this  sieve  after  which  it  may  be  quartered 
down  to  4  or  5  pounds. 

A  careful  and  painstaking  sampler  with  a  keen  eye  for  slate 
and  pyrite  may  if  all  such  particles  are  finely  crushed  quarter 
this  f-inch  portion  down  to  2  or  3  pounds  without  introducing 
any  error  of  consequence  since  portions  of  clean  coal  f-inch  in 
size  or  larger  have  little  influence  on  the  ash  and  sulphur  content. 
This  item  is  discussed  more  in  detail  under  "  Car  sampling." 

Working  down  the  sample  in  the  mine  is  however  too  often 
done  in  a  dim  light  and  hurriedly,  rather  than  under  favorable 
conditions  and  the  author  strongly  favors  a  minimum  division 
of  the  sample  in  the  mine  rather  than  the  division  to  the  smaller 
amounts.  The  10-pound  portion  of  the  J-inch  size  or  the  5- 
pound  portion  of  the  f-inch  size,  or  better  still  the  entire  sample 
if  not  reduced  should  be  sent  to  the  chemical  laboratory.  If 
the  moisture  result  is  unimportant  the  shipment  may  be  made 
in  a  closely  woven  canvas  bag.  If,  however,  the  moisture  is  of 
importance  the  shipment  must  be  made  in  a  closed  metal  or  glass 
container.  A  half  gallon  fruit  jar  suffices  for  the  smaller  sample 
but  a  metal  container  is  to  be  preferred  as  being  less  liable  to 
breakage,  in  which  case  a  J-gallon  galvanized  or  tin  container 
with  a  screw  top  for  the  small  sample  or  a  one-  to  four-gallon 


SAMPLING  61 

container  with  screw  top  for  the  larger  sample  is  satisfactory, 
the  screw  top  being  sealed  by  means  of  adhesive  tape  to  prevent 
moisture  loss. 

The  shipments  of  samples  by  the  Ohio  Geological  Survey  are 
made  in  galvanized  iron  cans  10x10x10  inches,  fitted  with  3j-inch 
screw  caps  or  tops.  One  of  these  cans  hold  about  40  pounds  of 
sample  and  allows  for  the  shipment  either  of  all  or  of  one-half  of 
the  sample  cut.  Well-constructed  wooden  cases  built  to  hold  four 
of  these  cans  are  used  in  shipping  the  samples  to  the  laboratory. 

If  nothing  better  is  at  hand  tall  tin  pails  or  cans  with  well- 
fitting  lids  may  be  used,  care  being  taken  to  tie  the  lids  very 
securely  on  to  the  pails  or  cans.  If  not  well  secured  they  may 
loosen  in  transit  and  where  several  samples  are  shipped  together 
in  the  same  box  all  may  be  spoiled  by  an  accident  of  this  kind. 
In  shipping  glass  cans  or  metal  containers  they  should  be  well 
packed  with  burlap,  paper  or  excelsior  in  order  to  lessen  danger 
of  breakage  in  transit. 

Portable  sampling  outfit.  Where  much  mine  sampling  is  to 
be  done  a  portable  sampling  outfit  is  almost  a  necessity.  The 
essential  articles  comprising  such  an  outfit  are  as  follows: 

Carrying  bag  or  container,  sampling  cloth  or  canvas,  mortar 
and  pestle,  sieves,  sampling  scoop,  brush  or  whisk  broom,  sam- 
pling cans,  adhesive  tape,  measuring  tape.  A  pick  and  shovel 
are  a  necessary  part  of  the  equipment  but  these  can  usually  be 
obtained  at  the  mine  and  are  not  included  as  such  as  a  part  of 
the  portable  outfit. 

Carrying  bag  or  container.  Any  container  which  will  hold  the 
outfit  will  do  and  the  simpler  the  better.  An  ordinary  canvas  sack 
is  very  satisfactory  and  the  outfit  can  be  carried  either  in  the  hand 
or  thrown  over  the  shoulder. 

Sampling  cloth.  This  should  be  of  durable  material  and 
impervious  to  -.water.  Closely  woven  16  to  20  oz.  duck  or  heavy 
enamelled  buggy  cloth  is  satisfactory.  If  the  enamelled  cloth  is 
used  it  should  be  used  enamelled  side  down.  The  cloth  must  not 
be  too  small.  The  author  prefers  a  cloth  about  7  feet  square. 

Portable  mortar.  The  mortar  at  present  used  by  the  Depart- 
ments of  Metallurgy  and  Mining  Engineering  at  the  Ohio  State 
University  is  constructed  as  follows:  The  mortar  block  consists 
of  a  Y^-inch  steel  plate  10  inches  in  diameter  on  which  is  mounted 
a  wooden  block  1J  inches  thick  and  to  this  is  attached  the  mortar 


62 


COAL 


plate  proper  of  J-inch  steel.  Each  plate  is  secured  to  the  wooden 
block  by  countersunk  screws.  The  lower  portion  of  the  sides  of 
the  mortar  are  formed  by  a  heavy  circular  piece  of  sole  leather 
2f  inches  wide  which  is  firmly  secured  by  screws  to  the  wooden 
block.  To  prevent  escape  of  coal  the  ends  of  the  leather  are 
tapered,  lapped  and  glued  together  with  waterproof  leather  cement. 
To  the  upper  portion  of  the  leather  is  attached  a  circular  piece 
of  16-ounce  canvas,  7J  inches  wide,  which  forms  the  upper  por- 
tions of  the  sides  of  the  mortar.  The  upper  edge  of  the  canvas 
is  attached  to  a  flat  steel  ring,  this  ring  being  connected  to  the 
mortar  base  by  collapsible  spring  steel  supports  held  in  position 


FIG.  1. — Portable  Sampling  Outfit. 

by  set  screws.  When  the  set  screws  are  loosened  the  supports 
and  canvas  fold  down  out  of  the  way,  the  loose  ends  of  the  spring 
steel  supports  being  secured  by  spring  clips  on  the  sides  of  the 
mortar  block. 

Pestle.  A  common  molder's  tamping  iron  3f  inches  in  diameter 
and  fitted  with  a  handle  12  inches  long  is  used. 

Sieve.  This  consists  of  a  galvanized  iron  frame  11  inches  in 
diameter  by  5  inches  high,  into  which  are  fitted  removable  screens 
of  different  sizes,  as  f,  i,  f  and  }  inch.  The  J-  and  f-inch  screens 
are  the  two  usually  used.  This  sieve  is  large  enough  to  hold  the 
mortar  when  the  outfit  is  packed  together. 

Sampling  scoop.  This  is  merely  a  heavy  piece  of  galvanized 
iron  resembling  a  small  dustpan  but  having  no  handle.  It  is 


SAMPLING  63 

used  for  quartering  down  and  mixing  and  also  for  scooping  up 
the  reserve  portion  of  the  sample. 

Broom.     A  small  6-inch  whisk  broom  is  very  satisfactory. 

Sampling  cans.  The  cans  at  present  used  by  the  Departments 
of  Metallurgy  and  Mining  Engineering  are  5  inches  in  diameter 
by  llf  inches  high  and  hold  from  8  to  10  pounds  of  sample.  They 
are  constructed  of  22  gauge  galvanized  iron  and  the  dimensions 
are  such  that  two  cans  fit  end  to  end  in  an  ordinary  24-inch  trunk. 

Adhesive  tape.  Ordinary  electrical  or  bicycle  tape  is  used  for 
sealing  the  lid  after  the  sample  has  been  put  into  the  can. 

Measuring  tape.  A  25-ft.  metallic  tape  graduated  to  fractions 
of  an  inch  is  useful  in  measuring  sections,  etc.  Fig.  1  is  an 
illustration  of  portions  of  the  above  described  outfit. 

The  outfit  used  by  the  U.  S.  Bureau  of  Mines  is  similar  to  the 
one  described  except  that  smaller  sampling  cans  are  used  and  a 
spring  balance  is  included  as  a  part  of  the  outfit.  An  experienced 
sampler  has  little  use  for  a  spring  balance  and  with  the  large 
sample  cans  the  amount  of  sample  cut  can  be  checked  up  in  the 
laboratory  from  the  weight  of  the  sample  and  from  the  data  given 
in  the  collector's  notes  as  to  what  aliquot  portion  of  the  sample 
is  represented  by  the  final  sample. 

For  details  of  the  Government  sampling  outfit,  see  Tech- 
nical Paper  No.  1,  Bureau  of  Mines,  Department  of  the  Interior. 

Car  sampling  and  sampling  coal  as  used.  Directions  for 
sampling  coal  in  a  car,  sampling  a  coal  as  unloaded  or  sampling 
coal  as  used  are  hard  to  formulate  owing  to  the  great  difference 
in  moisture,  ash  and  sulphur  and  in  the  physical  conditions  of 
different  lots  of  coal.  The  amount  of  sample  to  be  taken  depends 
upon  the  variations  in  these  factors  and  upon  the  amount  of  coal 
sampled  and  a  set  of  directions  which  might  give  satisfactory 
results  on  one  coal  if  used  on  an  entirely  different  coal  might  be 
very  unsatisfactory;  and  a  set  of  directions  for  sampling  a  bad 
lot  of  coal  would  be  unnecessarily  expensive  if  used  to  sample  a 
comparatively  uniform  coal. 

The  common  method  of  obtaining  a  sample  of  coal  during  a 
boiler  test  is  as  follows:  As  each  lot  of  coal  is  weighed,  portions 
taken  from  various  parts  are  put  into  a  closed  barrel,  box  or  a 
metal  container  with  a  closely  fitting  cover,  an  effort  being  made 
to  get  an  average  of  fine  and  lump  coal.  The  amount  of  sample 
taken  in  this  way  in  a  day's  run  where  5  or  6  tons  of  coal  are 


64  COAL 

fired  should  be  from  100  to  300  pounds,  depending  upon  the  coal. 
If  clean  slack  or  washed  nut  coal,  the  smaller  amount  may  be 
satisfactory.  If  ash  and  sulphur  are  present  in  considerable 
amounts  and  especially  if  in  the  form  of  slate  and  pyrite,  the 
larger  quantity  should  be  taken.  In  sampling  a  car  as  unloaded 
the  same  method  should  be  used,  small  portions  being  taken  at 
regular  intervals  during  the  unloading,  the  amount  taken  vary- 
ing with  the  coal,  500  or  600  pounds,  if  the  coal  is  run-of-mine 
to  as  low  as  200  pounds  if  fine  slack  or  clean  nut. 

Reduction  of  the  large  sample.  The  entire  sample  taken 
(200  to  600  pounds)  should  be  spread  upon  a  clean  floor,  the  large 
pieces  of  coal,  slate  and  pyrite  crushed  with  a  hammer  and  a 
heavy  iron  plate  till  the  largest  particles  of  slate  and  pyrite  do 
not  exceed  J  inch.  This  requires  that  the  sample  be  gone  over 
repeatedly  with  a  shovel  so  as  to  bring  all  portions  to  the 
view  of  the  sampler.  It  should  then  be  thoroughly  mixed 
and  divided  into  quarters.  The  two  opposite  quarters  should  be 
brushed  to  one  side  with  a  broom.  The  two  remaining  quarters 
should  be  again  mixed,  any  chunks  of  slate  and  pyrite  crushed 
still  finer  and  the  sample  again  divided  by  quartering.  With 
careful  crushing  of  slate  and  pyrite  this  quartering  can  be  repeated 
a  third  time  if  desired.  The  last  portion  of  sample  amounting 
to  60  to  80  pounds,  should  be  sent  to  the  chemical  laboratory 
for  further  treatment.  If  a  power  crusher  or  pulverizer  is  avail- 
able—and where  much  sampling  is  to  be  done  such  a  machine 
is  almost  a  necessity — the  entire  600  pounds  should  be  put  through 
this  pulverizer  which  can  be  set  to  reduce  it  to  a  fineness  of  about 
J  inch  and  finer,  in  which  case  the  sample  can  be  quartered  down 
repeatedly  and  the  sample  sent  to  the  laboratory  need  not  exceed 
4  or  5  pounds. 

The  chute  through  which  the  crushed  sample  passes  after 
being  put  through  the  pulverizer  may  easily  be  arranged  to 
mechanically  divide  the  sample  by  an  arrangement  of  partitions 
to  successively  divert  aliquot  parts,  so  that  the  final  portion 
diverted  is  small  enough  to  be  sent  to  the  laboratory  without 
further  handling.  (See  Fig.  2.)  The  space  below  the  end  of  the 
chute  must  of  course  be  sufficient  to  accommodate  a  container 
for  holding  the  portion  of  the  sample  which  passes  through. 
For  example,  with  samples  up  to  600  pounds  and  |  passing 
through  the  chute  the  receiving  bucket  should  hold  not  less  than 


SAMPLING 


65 


FIG.  2. — Sampling  Chute. 


66  COAL 

80  pounds  of  coal.  In  order  to  further  divide  this  80-pound 
sample,  an  auxiliary  hopper  may  be  connected  to  the  top  of  the 
chute  and  the  sample  again  divided  by  passing  through  the  chute 
a  second  time.  If  desired  the  divisions  in  the  chute  can  be  ar- 
ranged so  that  only  YG  of  the  sample  passes  through  and  for  large 
samples — 1000  pounds  or  more — this  is  desirable  in  that  it  avoids 
the  handling  of  excessively  heavy  samples  in  the  second  subdi- 
vision. One  laboratory  fitted  with  a  sampling  chute  similar  to 
the  one  described  has  a  revolving  cylindrical  mixer  between  the 
pulverizer  and  the  sampling  chute.  The  author  doubts  that  this 
is  any  decided  real  improvement  as  the  mixing  in  the  pulverizer 
is  certainly  thorough.  With  the  pulverizer  fitted  with  a  bar 
screen,  the  usual  equipment,  the  pulverized  sample  escapes  from 
the  crusher  evenly  across  the  face  of  the  screen  and  in  turn  is 
distributed  uniformly  in  the  top  of  the  chute. 

In  the  arrangement  shown  in  Fig.  2  the  discarded  portions 
of  the  sample  are  collected  in  the  small  bins  and  must  be  removed 
with  a  shovel  by  hand.  When  the  elevation  of  the  pulverizer  is 
sufficient  the  chutes  may  be  arranged  to  deliver  into  a  common 
bin  of  larger  capacity  which  need  be  emptied  only  occasionally. 
A  still  more  efficient  arrangement,  where  the  amount  of  sampling 
to  be  done  warrants  the  installation,  is  to  have  these  discarded 
portions  of  the  samples  removed  mechanically  by  having  the  chutes 
deliver  them  on  to  a  belt  conveyor.  Mechanical  arrangements 
for  conveying  the  sample  to  the  pulverizer  are  likewise  desirable 
when  large  amounts  of  sample  are  to  be  handled. 

In  quartering  down  by  hand  the  work  should  be  done  as 
rapidly  as  is  consistent  with  good  work  and  should  be  done  pref- 
erably in  a  cool  room  so  as  to  make  the  moisture  losses  as  small 
as  possible  and  the  portion  of  the  sample  sent  to  the  chemical 
laboratory  should  be  sent  in  a  closed  container.  Reduction  of 
the  sample  in  a  power  pulverizer  is  not  only  more  satisfactory 
on  account  of  the  finer  reduction,  of  the  coarse  sample  but  the 
crushing  being  done  rapidly  the  chances  of  moisture  loss  are  like- 
wise reduced. 

The  effects  of  particles  of  slate  and  pyrite  upon  the  sample. 
These  may  be  perhaps  best  shown  in  tabular  form  and  serve  to 
emphasize  and  make  clear  the  precautions  to  be  observed  in 
sampling.  Pyrite  has  a  specific  gravity  of  about  5,  contains 
about  53  per  cent  of  sulphur  and  on  burning  forms  the  equiv- 


SAMPLING 


67 


alent  of  65  per  cent  of  ash.  Slate  and  shale  have  a  specific  gravity 
of  about  2J  and  the  ash  may  run  as  high  as  80  per  cent.  A  piece 
of  pyrite  one  inch  each  way  weighs  approximately  80  grams  (3  oz.) 
and  contains  the  equivalent  of  42  grams  (1.6  oz.)  of  sulphur  and 
the  equivalent  of  52  grams  (1 .9  oz.)  of  ash,  the  weight  and  equivalent 
amounts  of  sulphur  and  ash  in  pieces  of  pyrite  equivalent  "to  cubes 
of  varying  sizes  larger  and  smaller  than  one  inch  are  as  follows : 


Size  in  Inches. 

Pyrite 
Weight  in  Grams. 

Sulphur 
Weight  in  Grams. 

Ash 
Weight  in  Grams. 

2 

640 

336 

416 

1 

-      80 

42 

52 

1 

10 

5.25 

6.5 

f 

4.22 

2.21 

2.7 

i 

4 

1.25 

0.656 

0.81 

i 

0.156 

0.082 

0.10 

i 

16 

0.0195 

0.0103 

0.012 

A 

0.00244 

0.0013 

0.0015 

A 

0.00031 

0.00016 

0.00019 

On  a  one-gram  sample  reduced  to  such  a  size  that  the  largest 
single  particle  of  pyrite  does  not  exceed  ^j  inch  the  weight  of  sulphur 
and  ash  equivalent  to  a  single  particle  is  0.00019  ash  and  0.00016 
sulphur.  Hence  the  results  on  a  one-gram  sample  containing  par- 
ticles of  this  size  will  be  too  high  or  too  low  by  0.016  per  cent  on 
sulphur  and  0.019  per  cent  on  ash  for  each  particle  more  or  less 
than  the  true  average  which  is  contained  in  the  sample  as  weighed. 

If  this  proportionate  weight  of  the  largest  size  pieces  to  the 
total  amount  of  sample  be  observed  for  pieces  of  pyrite  equiv- 
alent to  cubes  of  different  sizes,  approximately  the  following 
amounts  of  sample  must  be  taken  for  each  size: 


Size  in  Inches. 

Sample  Weight  in  Grams. 

Sample  Weight. 

? 

1 

-gV     ounces 

8 

2 

7 

JL 

64 

2| 

1 

510 

1  1-     poi 

nda 

I 

4090 

9 

1 

13700 

30 

32700 

72 

1 

260000 

570 

2 

2100000 

4600           ' 

3 

16800000 

37000 

68  COAL 

The  preservation  of  this  ratio  on  the  basis  of  the  largest  pieces 
of  pyrite  being  three  inches  in  size  means  that  practically  the 
whole  car  has  to  be  taken  as  the  sample  and  in  those  cases  where 
pyrite  occurs  as  sulphur  balls  several  inches  in  diameter  or  the 
slate  occurs  in  great  chunks  it  is  impossible  to  secure  a  repre- 
sentative sample  by  taking  only  a  small  amount  of  sample  from 
the  car.  Fortunately,  however,  the  slate  and  pyrite  present  in 
the  coal  as  marketed  usually  occur  in  smaller  particles  and  a 
500-  or  600-pound  sample  with  care  being  observed  that  no  large 
lumps  of  slate  and  pyrite  are  present  ought  to  be  satisfactory 
for  most  coal  samples  as  far  as  slate  and  ash  are  concerned. 

It  must  not  be  assumed  that  this  possible  accuracy  in  samp- 
ling of  only  one  piece  too  many  or  too  few  will  be  actually 
obtained  in  practice.  Working  down  the  large  sample  to  the 
small  laboratory  sample  requires  that  the  quartering  operation 
be  performed  8  or  10  times  and  the  composition  of  the  reserve 
portion  at  each  operation  is  somewhat  different  from  the  true 
average  of  the  whole  sample  taken.  If  the  quartering  is  properly 
done  these  variations  from  the  true  average  ought  to  be  both 
higher  and  lower  and  hence  tend  to  partially  eliminate  each 
other  and  the  composition  of  the  final  portion  should  approxi- 
mate that  of  the  original  sample.  Failure  to  properly  mix  and 
quarter  the  sample  may,  however,  result  in  the  accumulation  of 
these  errors  in  one  direction.  For  example,  a  failure  to  carefully 
sweep  away  the  heavy  particles  of  the  rejected  portions  wrould 
tend  to  produce  a  final  sample  containing  more  than  its  share  of 
heavy  particles. 

The  diameter  of  the  wires  composing  the  sieves  cuts  down  the 
actual  size  of  the  openings  from  10  to  15  per  cent  on  the  larger 
sizes  to  as  much  as  50  per  cent  on  the  fine  sieves  and  the  actual 
volume  of  particles  passing  through  the  different  mesh  sieves 
(if  the  mesh  is  uniform)  compared  to  the  volume  calculated  is 
only  f  to  \  for  the  larger  sizes  down  to  as  low  as  f  for  the  finer 
sieves,  hence  the  sampling  conditions  are  actually  more  favor- 
able than  is  shown  by  the  calculation.  However,  this  is  much  more 
than  offset  by  the  fact  that  in  practice  a  variation  of  only  one 
particle  from  the  true  average  cannot  be  obtained  and  in  actual 
sampling  an  accuracy  varying  with  the  coal  and  with  the  skill 
and  care  of  the  sampler  of  from  0.03  to  0.20  per  cent  on  sulphur 
and  from  0.05  to  0.5  per  cent  on  ash  is  to  be  regarded  as  good 


SAMPLING  69 

sampling.  The  lower  values  apply  to  clean  coal  low  in  ash  and 
low  in  sulphur.  The  higher  values  apply  to  coal  high  in  slate  and 
pyrite  and  with  improper  mixing  and  failure  to  crush  the  slate 
and  pyrite  the  actual  errors  on  such  coals  may  be  much  greater, 
errors  of  1  to  3  per  cent  for  ash  and  0.3  to  0.5  per  cent  for  sul- 
phur being  far  too  common  in  ordinary  sampling  practice. 

The  passing  of  the  final  laboratory  sample  through  a  60-mesh 
sieve  insures  a  fineness  of  this  final  product  which  in  proportion 
to  the  sample  weighed  out  is  greater  than  for  the  larger  bulk 
samples,  as  with  a  uniform  60-mesh  sieve  the  largest  particles 
passing  through  probably  do  not  exceed  -fa  to  TO~O  inch  in  diameter, 
and  the  ratio  of  the  largest  particle  of  this  size  to  a  one-gram 
sample  is  2  or  3  times  the  calculated  ratio  of  a  ^j-inch  particle. 
Hence  as  far  as  duplicate  determinations  on  the  actual  laboratory 
samples  are  concerned,  results  ought  to  be  and  are  much  closer 
than  can  be  expected  on  duplicates  of  the  larger  samples. 

Effect  of  large  pieces  of  clean  coal  upon  the  sample.  Large 
lumps  of  clean  coal  will  not  seriously  affect  the  average  of  the  ash 
and  sulphur  in  the  sample  and  while  it  certainly  is  not  advisable 
to  include  without  breaking  down  lumps  of  clean  coal  8  inches 
in  diameter  in  a  sample,  the  effect  of  such  a  lump  of  clean  coal 
on  a  600-pound  sample  would  not  be  very  serious.  For  example, 
a  lump  of  coal  8  inches  each  way  weighs  about  20  pounds. 
Assuming  that  this  lump  analyzes  5  per  cent  ash  and  1  per  cent 
sulphur  and  that  the  true  average  of  the  shipment  is  10  per  cent 
ash  and  2  per  cent  sulphur,  then  this  lump  will  affect  the  true 
ash  percentage  as  follows:  10  per  cent  on  600  pounds  =  60  pounds 
of  ash — the  correct  amount;  10  per  cej^t  of  ash  on  580  pounds 
=  58  pounds  of  ash  and  5  per  cent  of  ash  on  20  pounds  =  1  pound 
of  ash  or  a  total  of  59  pounds  of  ash  for  the  600  pounds  of  sample 
containing  the  large  lump  of  clean  coal,  a  percentage  of  9.83 
instead  of  10— the  correct  percentage.  On  the  other  hand,  a  piece 
of  shale  8  inches  each  way  containing  75  per  cent  ash  and  weigh- 
ing 40  pounds  would  affect  the  true  result  as  follows :  560  pounds 
of  coal  with  10  per  cent  ash  =  56  pounds;  40  pounds  of  shale 
with  75  per  cent  of  ash  =  30  pounds  of  ash  or  a  total  of  86  pounds 
of  ash  in  the  600-pound  sample  containing  the  large  lump  of 
shale,  a  percentage  of  14.3  ash  instead  of  10 — the  correct  per- 
centage. 

The  sampler  must,  therefore,  use  common  sense  and  discre- 


70  COAL 

tion  in  sampling  rather  than  to  sample  by  a  rigid  rule.  Common 
sense  and  discretion  mean  to  guard  against  moisture  losses  and 
to  look  out  for  large  pieces  of  slate  and  pyrite,  to  break  them 
down  fine  and  to  try  to  get  as  near  as  possible  a  fair  proportion  of 
each  in  the  sample. 

Relation  of  amount  of  car  sample  to  the  number  of  cars 
sampled.  Where  a  number  of  cars  are  sampled  and  the  results  of 
the  analysis  of  the  mixed  samples  is  the  basis  of  settlement  for  the 
entire  shipment,  the  amount  of  coal  taken  from  each  individual  car 
may  be  considerably  less  than  where  only  one  car  is  sampled  as  the 
errors  in  the  different  samples  will  to  a  considerable  extent  tend 
to  balance  each  other  provided  a  proper  method  of  sampling  is 
used.  For  example,  if  500  pounds  is  required  to  secure  a  repre- 
sentative sample  from  a  single  car,  to  se"cure  an  equally  repre- 
sentative sample  from  10  cars,  it  is  not  necessary  to  take  500 
pounds  from  each  car.  The  average  of  samples  of  200  pounds 
from  each  car  should  be  as  close  to  the  true  composition  of 
the  coal  in  the  10  cars  as  the  analysis  of  500  pounds  from  any 
single  car  is  to  the  true  composition  of  the  coal  in  the  single  car, 
since  the  errors  in  the  ten  samples  will  to  a  large  degree  counter- 
balance each  other.  This  is  true,  however,  provided  that  the 
sampling  is  properly  done.  If  the  sampling  is  improperly  done 
the  errors  in  the  individual  samples  are  all  liable  to  be  in  the 
same  direction  and  hence  the  average  of  any  number  of  such 
samples  will  not  represent  a  true  average  of  the  shipment.  The 
taking  of  samples  from  the  top  of  a  car  only  is  to  be  strictly 
avoided  as  almost  certain  to  introduce  systematic  errors. 

TREATMENT  OF  THE  SAMPLE  IN  THE  CHEMICAL 
LABORATORY 

Air  drying.  Upon  arrival  at  the  laboratory,  if  necessary,  the 
sample  should  be  reduced  by  crushing  to  about  J  inch  and  finer 
and  quartered  down  to  4  to  6  pounds.  This  portion  should  then 
be  weighed  and  allowed  to  thoroughly  air  dry  by  standing  exposed 
to  the  air  of  the  room  for  36  hours  or  longer  or  by  putting  in  a 
drier  heated  to  a  temperature  of  10  or  15  degrees  above  the  room 
temperature  and  having  adequate  circulation  of  air,  in  which  case 
the  drying  can  usually  be  completed  in  six  to  eight  hours.  (See 
Fig.  3.)  This  air  drying  should  be  continued  until  two  weigh- 


SAMPLING 


71 


ings  made  at  intervals  of  \  day  or  so  if  dried  in  the  labora- 
tory or  two  hours  or  more  if  dried  in  the  drier  show  less  than 
\  per  cent  loss  in  weight.  The  more  thorough  by  the  air  drying  is 
done  the  less  the  finely  ground  laboratory  sample  is  liable  to 
change.  The  total  loss  in  weight  is  reported  as  air  drying  loss. 
Reduction  of  sample.  After  air  drying,  the  sample  should 
be  reduced  by  passing  through  crushing  rolls  or  by  means  of  a 


FIG.  3. — Drier  for  Coarse  Samples. 

bucking  board  until  it  passes  an  8-mesh  sieve  at  which  point  it 
may  belquartered  down  to  about  1  pound.  This  should  be  still 
further  reduced,  if  necessary,  until  it  will  pass  a  10-mesh  sieve. 
It  may  then  be  quartered  down  to  J  to  f  pound  and  reduced  to  a 
powder  in  a  pebble  mill  or  in  the  absence  of  a  pebble  mill  bucked 
down  on  a  bucking  board  until  a  1-  or  2-ounce  sample  is 
obtained  which  will  pass  a  60-mesh  sieve.  This  bucking  board 
sample,  or  about  a  2-ounce  portion  of  the  well-mixed  sample 
from  the  pebble  mill,  should  be  placed  in  a  wide-mouth  4-ounce 


72  COAL 

bottle  and  well  stoppered.  This  constitutes  the  laboratory 
sample. 

For  the  fine  grinding  the  author  prefers  a  pebble  mill,  for 
coals  containing  much  moisture.  The  jars  used  are  7  inches 
in  diameter  by  7  inches  high  inside.  The  pebbles  used  are 
about  1  inch  in  diameter.  For  this  size  jar  a  speed  of  from  55 
to  60  revolutions  a  minute  gives  good  results,  a  three-fourth- 
pound  sample  being  reduced  from  one-eighth  inch  to  one-sixtieth 
inch  in  from  30  to  35  minutes.  At  the  end  of  the  grinding  opera- 
tion the  jar  is  opened  and  the  sample  is  separated  from  the  peb- 
bles by  pouring  the  contents  of  the  jar  upon  a  coarse  sieve. 

The  fine  sample  of  coal  is  divided  down  to  about  2  ounces 
by  passing  through  a  small  riffle  sampler  or  the  sample  is  thor- 
oughly mixed  by  hand  with  a  spatula  and  about  2  ounces  taken 
with  a  sampling  spoon  from  various  parts  of  the  material.  This 
2-ounce  portion  is  then  put  through  the  60-mesh  sieve  and  kept 
well  covered  during  the  sifting  to  prevent  moisture  changes.  A 
light  flat  brass  ring  (about  2  inches  in  diameter  and  weighing 
about  4  ounces)  placed  in  the  sieve,  is  of  very  great  assist- 
ance in  sifting  the  sample,  preventing  caking  of  the  material  and 
clogging  of  the  meshes  of  the  sieve.  Usually  a  few  coarse  par- 
ticles, amounting  to  from  one-fourth  to  one-half  per  cent  of  the 
sample,  remain  upon  the  sieve.  These  are  bucked  down  by  hand 
on  a  bucking  board  and  thoroughly  mixed  with  the  sifted  portion 
of  the  sample.  The  whole  is  then  put  in  a  glass  bottle  and 
securely  stoppered  and  constitutes  the  laboratory  sample  for 
analysis. 

The  jars  and  pebbles  after  being  cleaned  by  brushing  with  a 
stiff  brush  (this  part  of  the  operation  requiring  only  a  minute 
or  so)  are  ready  for  the  grinding  of  another  sample  of  coal.  When 
samples  of  entirely  materials  are  ground,  the  jars  and  pebbles 
may  require  more  thorough  cleansing  with  water  and  scrub 
brush,  but,  as  a  rule,  in  their  use  for  coal,  dry  cleansing  is 
sufficient. 

The  riffle  sampler  used  in  reducing  the  sample  is  shown  in 
figure  4.  Two  sizes  of  sampler  are  used  in  the  laboratory.  The 
larger  size  has  one-inch  subdivisions  and  is  used  in  reducing  the 
sample  from  25  pounds  down  to  the  amount  to  be  ground  in  the 
ball  mill  (about  three-fourths  pound).  The  sample,  after  grind- 
ing in  the  ball  mill,  is  divided  down  to  about  2  ounces  by 


SAMPLING 


73 


means  of  the  smaller  sampler  having  one-half  inch  subdivi- 
sions. 

The  sampler  is  essentially  a  metal  box  mounted  on  legs  and 
fitted  with  a  number  of  equidistant  vertical  parallel  partitions, 
the  alternate  bottoms  of  the  spaces  between  the  partitions  slop- 
ing in  opposite  directions.  The  angle  of  slope  should  be  about 
60°  from  the  horizontal.  If  much  less  than  this  the  coal  will  not 
run  freely  and  may  clog  the  sampler. 

The  lower  portions  of  the  sides  of  the  sampler  are  open  and 


FIG.  4. — Riffle  Sampler. 

the  coal  emptied  in  the  top  of  the  sampler  runs  down  the  sloping 
bottoms  of  the  subdivisions  and  is  caught  in  two  buckets  below, 
one-half  of  the  sample  being  caught  in  each  bucket.  To  keep 
down  dust  the  space  above  the  receiving  buckets  is  covered  with 
a  metal  hood  or  shield.  Three  buckets  are  necessary  for  con- 
venience in  sampling,  two  to  set  under  the  sampler  and  the  third 
to  contain  the  portion  of  the  sample  to  be  subdivided.  After 
pouring  the  material  through  the  sampler  one  of  the  buckets 
containing  one-half  of  that  poured  through  is  removed  and  the 
empty  bucket  set  in  its  place.  The  one-half  portion  is  then 


74  COAL 

poured  through  in  turn.  The  bucket  last  set  under  containing 
one  quarter  of  the  original  sample  is  removed  and  the  empty 
one  again  set  in  its  place,  the  subdivision  of  the  sample  being 
continued  till  the  sample  is  reduced  to  the  amount  desired. 

After  dividing  a  sample,  the  sampler  is  most  conveniently 
cleaned  by  directing  a  blast  of  air  from  a  handbellows  through 
the  subdivisions  and  any  particles  of  material  clinging  to  the 
sides  or  the  bottoms  of  the  divisions  removed  before  the  appara- 
tus is  used  for  dividing  another  sample. 

SPECIAL  NOTES   ON   SAMPLING 

Fineness  of  final  sample.  Coals  unusually  high  in  pyrite 
and  slate  should  perhaps  preferably  be  put  through  an  80-mesh 
sieve  rather  than  through  the  60-mesh  but  the  author  is  of  the 
opinion  that  the  60-mesh  is  amply  fine  for  nearly  all  samples. 
Grinding  to  100-mesh  and  finer  is  to  be  avoided  as  the  more  rapid 
oxidation  of  the  fine  sample  may  and  in  some  samples  certainly 
does  affect  the  results  obtained  for  calorific  value  and  the  ulti- 
mate composition.  Where  the  sample  is  ground  in  a  ball-mill 
the  grinding  should  be  continued  only  long  enough  to  insure  the 
desired  fineness  of  60-mesh  and  finer.  If  left  in  a  longer  time  the 
sample  will  be  ground  excessively  fine  and  subject  to  the  larger 
oxidation  changes  mentioned. 

Grinding  of  coals  containing  appreciable  amounts  of  mois- 
ture. With  coals  containing  appreciable  amounts  of  moisture 
it  is  safer  in  case  the  sampling  is  done  on  the  bucking  board  to 
reserve  a  2-ounce  portion  of  the  10-mesh  size  for  the  moisture  deter- 
mination. Plenty  of  time  may  then  be  taken  for  sampling  the 
bucking  board  sample  and  in  fact  it  is  a  better  laboratory  sample 
if  spread  out  and  dried  for  a  considerable  period  of  time  before 
being  put  into  the  sample  bottle.  The  analytical  results  obtained 
upon  this  sample  must  be  reduced  to  the  moisture  content  in  the 
coarse  sample  obtained  by  determining  the  moisture  on  a  5-  or  10- 
gram  portion  of  the  10-  or  20-mesh  sample. 

It  is  often  assumed  with  a  well  air  dried  coarse  sample  that  there 
is  no  danger  from  moisture  changes  in  bucking  down  the  fine 
sample  on  the  bucking  board.  This,  however,  is  a  false  assump- 
tion as  the  results  of  numerous  experiments  on  different  coals  have 
shown  that  fine  samples  of  coal  give  up  or  take  up  considerable 


SAMPLING  75 

moisture  with  changes  in  the  humidity  and  temperature  of  the 
sampling  room.  A  large  number  of  experiments  on  this  point  are 
given  in  Bulletin  No.  323  of  the  U.  S.  Geological  Survey  which  is 
published  as  a  reprint  by  the  Bureau  of  Mines  as  Bulletin  No.  28. 
A  large  number  of  comparisons  of  the  bucking  board  samples  and 
the  ball-mill  samples,  sampled  under  observed  conditions  of  tem- 
perature and  humidity  are  recorded.  These  comparisons  show 
losses  in  the  bucking  board  samples  in  some  cases  as  great  as  2  per 
cent.  In  other  cases  where  the  air  drying  of  the  coarse  samples 
had  been  a  little  too  thorough  the  bucking  board  samples  showed 
increases  in  moisture,  in  some  cases  amounting  to  0.6  per  cent. 
These  results  are  all  upon  the  air  dried  samples  which  were  pre- 
sumably close  to  an  air-dry  condition. 

The  moisture  losses  upon  bucking  board  samples  of  undried 
coal  may  easily  be  4  to  5  per  cent  with  coals  at  all  high  in  mois- 
ture. Laboratory  experiments  on  a  fine  sample  of  Illinois  coal 
containing  12.4  per  cent  moisture  showed  for  a  one-gram  sample 
spread  on  a  watch  glass  and  exposed  to  the  laboratory  air  a  loss 
of  2  per  cent  in  5  minutes.  As  the  time  required  to  buck  down  a 
fine  sample  on  a  bucking  board  is  often  several  times  5  minutes 
the  moisture  losses  on  such  samples  cannot  be  otherwise  than  of 
considerable  magnitude.  A  sample  of  Illinois  coal,  the  coarse 
sample  of  which  had  previously  been  well  air-dried,  showed  a 
loss  of  0.93  per  cent  after  5  minutes'  exposure  to  the  laboratory 
air  with  a  total  moisture  content  of  only  4.12  per  cent  in  the 
sample,  from  which  the  conclusion  that  bucking  board  samples 
even  on  well  air-dried  samples  are  not  entirely  satisfactory  seems 
to  be  if  anything  conservative.  With  low  moisture  coals  such  as 
some  of  the  Arkansas  and  West  Virginia  coals  the  moisture  losses 
on  bucking  board  samples  from  the  well  air-dried  samples  are  not 
likely  to  be  very  large,  the  experiments  recorded  showing  mois- 
ture losses  or  changes  of  only  0.1  or  0.2  per  cent;  but  in  higher 
moisture  coals  such  as  Illinois,  Indiana,  or  Ohio  the  bucking 
board  samples  cannot  be  regarded  as  entirely  satisfactory. 

Omitting  the  air-drying  on  the  coarse  sample.  When  this 
is  done  the  reservation  of  a  portion  of  the  10-mesh  sample  for  the 
moisture  determination  is  essential  if  the  moisture  percentage 
and  the  calorific  value  are  desired.  If  only  ash  and  sulphur 
results  are  desired,  in  many  coals,  failure  to  correct  to  "  moisture 
as  received  "  may  not  be  important.  When  preliminary  air 


76  COAL 

drying  of  the  coarse  sample  is  omitted  the  weighing  of  the  fine 
sample  in  the  laboratory  must  be  done  quickly  as  serious  mois- 
ture losses  may  occur  and  mixing  of  such  a  sample  on  paper  pre- 
vious to  weighing  should  be  strictly  prohibited  as  moisture  losses 
are  sure  to  result. 

Bucking  board  grinding.  While  slower  than  power  grinding, 
if  used  in  connection  with  power  crushing  and  the  crushing  rolls, 
the  reduction  of  the  sample  is  not  excessively  tedious,  but  if  the 
bucking  board  is  used  to  grind  down  a  sample  from  J  inch  or  larger, 
it  is  considerably  slower  on  account  of  the  much  larger  amount  of 
sample  to  be  reduced,  and  a  great  danger  of  bucking  board  sam- 
pling is  too  much  quartering  down  of  the  rather  coarse  sample. 
The  crushing  rolls  and  ball-mill  avoid  this  tendency  entirely 
and  are  to  be  preferred  on  this  account  as  well  as  on  account  of 
smaller  moisture  changes. 

Necessity  of  making  analytical  determinations  on  the  fine 
sample  without  undue  delay.  The  analytical  work  upon  the 
laboratory  sample  should  be  done  promptly  as  fine  samples  of  coal 
are  known  to  undergo  considerable  oxidation  changes.  Exper- 
iments recorded  in  the  bulletin  just  referred  to  show  oxidation 
changes  amounting  to  as  much  as  2J  per  cent  of  the  original 
weight  of  the  coal  during  a  period  of  eight  months.  These  oxida- 
tion changes  took  place  on  samples  well  stoppered  with  rubber 
stoppers.  Where  the  sample  has  more  or  less  free  exposure  to  air 
the  oxidation  changes  are  almost  certain  to  be  of  considerable 
magnitude.  Certainly  reliable  results  cannot  be  obtained  upon 
a  sample  which  have  stood  around  the  laboratory  for  any  great 
length  of  time. 

Equipment  for  reduction  of  samples.  The  equipment  used  by 
the  author,  some  of  which  has  already  been  described  and  which 
he  has  found  satisfactory,  is  as  follows: 

(1)  A    swing  hammer  pulverizer  equipped  with  a  chute  for 
mechanically  dividing  the  samples.     Such  a  pulverizer  readily 
reduces  large  samples  to  J  inch  and  the  samples  can  be  divided 
down  to  4  or  5  pounds  without  further  treatment. 

(2)  A  hand  or  power  jaw  crusher  for  reducing  coal  samples 
to  J  inch  is  very  satisfactory,  but  for  rapid  reduction  of  large 
samples  of  coal  the  author  prefers  the  pulverizer.     For  small 
samples — 25  pounds  or  less —  a  hand  jaw  crusher  is  satisfactory 
but  for  large  samples  power  crushers  of  larger  capacity  are  pref- 


SAMPLING  77 

erable.  It  is  hardly  necessary  to  state  that  an  ordinary  labora- 
tory does  not  need  a  power  equipment  of  both  crusher  and 
pulverizer. 

(3)  For  crushing  the  J-inch  samples  to  10-mesh  a  pair  of  6-inch 
power  rolls  are  efficient,  rapid  and  satisfactory. 

(4)  For  reduction  of  the  10-mesh  samples  to  60-mesh  and  finer 
a  pebble  mill  is  very  efficient  and  prevents  moisture  changes 
during  pulverizing. 

(5)  For  occasional  sampling  an  ordinary  bucking  board  with 
a  rather  heavy  muller  answers  the  purpose. 

(6)  For  air  drying  of  coarse  samples  previous  to  pulverizing 
a  drying  oven  similar  to  the  one  shown  in  figure  3  is  very  satis- 
factory.   The  trays  of  this  drier  are  of  galvanized  iron  1  inch 
deep  by  24  by  24  inches. 

(7)  In  weighing  up  the  air-dried  samples  on  the  large  trays  a 
Troemner  solution  scale  No.  80  is  very  satisfactory. 

(8)  For  mechanical  dividing  of  the  samples,  riffle  samplers 
similar  to  that  shown  in  figure  4  are  satisfactory. 

(9)  Coarse  wooden  frame  sieves  from  one  inch  to  J-inch  and 
brass  sieves  from  10-mesh  to  80-mesh  are  a  necessary  part  of  the 
equipment. 

The  particular  machines  used  by  the  author  are  as  follows 
and  have  proven  satisfactory.  Similar  machines  of  other  makes 
are  doubtless  equally  as  efficient. 

(1)  Jeffrey  "  baby  pulverizer  "  manufactured  by  the  Jeffrey 
Manufacturing    Company,    of    Columbus,    Ohio.      Horse-power 
required  6  to  8.    The  "  baby  pulverizer  "  easily  has  a  capacity  of 
over  1000  pounds  per  hour. 

(2)  Chipmunk  jaw  crusher,  manufactured  by  F.  W.  Braun 
&  Co.,  Los  Angeles,  California.     Horse-power  required   1  to  2. 
The  jaw  crushers  have  a  capacity  per  hour  of  about  200  pounds 
for  the  smaller  size  to  about  1000  pounds  for  the  larger  size. 

(3)  Six-inch   crushing  rolls  manufactured  by  the  American 
Concentrator  Company,  Joplin,   Mo.     The  crushing   rolls  have 
ample   daily  capacity  for  any  ordinary  requirement.     Allowing 
time  for  cleaning  between  grinding  of  samples  if  run  to  capacity 
50  to   100  samples  of  four  or  five   pounds  each  can  easily  be 
reduced  by  the  rolls  from  J  inch  to  10-mesh  and  finer. 

(4)  Four-jar  ball-mill  manufactured  by  the  Abbe  Engineer- 
ing Company,  New  York.    The  four-jar  ball-mill  if  provided  with 


78  COAL 

an  extra  set  of  jars  and  kept  running  to  capacity  will  grind  40  to 
50  samples  per  day. 

(5)  The  drier,  riffle  sampler,  etc.,  can  readily  be  constructed 
by  local  tinsmiths.  The  drier  described,  see  figure  3,  holds  only 
eight  large  samples  but  if  supplemented  by  air  drying  of  samples 
over  night  15  to  20  samples  per  day  can  be  dried  ready  for  final 
grinding.  If  a  larger  number  of  samples  are  to  be  handled  a  larger 
drier  should  be  provided. 


CHAPTER  IV 
METHODS  OF  ANALYSIS 

•  THE  samples  from  the  sampling  room  or  laboratory  should 
be  sent  to  the  chemical  laboratory  in  wide-mouth  bottles  securely 
closed  with  rubber  stoppers.  Ordinary  4-ounce  wide-mouth  bot- 
tles are  very  convenient  for  coal  samples. 

Weighing  out  a  Sample  for  a  Determination.  In  weighing 
out  portions  of  the  laboratory  sample  for  a  determination,  the 
sample  should  be  well  mixed.  An  efficient  method  of  mixing  is  as 
follows:  The  material  is  thoroughly  mixed  by  giving  the  bottle 
15  to  20  rotations  with  an  upending  and  tilting  movement  of  the 
bottle  to  insure  mixing  of  the  top  and  bottom  portions  of  the 
sample.  For  satisfactory  mixing  in  this  way  the  sample  should 
not  fill  the  bottle  more  than  half  full.  After  the  mixing  in  the 
bottle  the  stopper  is  removed  and  the  sample  still  further  mixed 
by  means  of  a  sampling  spoon  and  successive  small  portions  taken 
until  the  amount  required  for  the  determination  is  secured,  espe- 
cial care  being  taken  to  again  securely  stopper  the  bottle  before 
setting  it  aside  for  other  determinations.  If  the  sample  more 
than  half  fills  the  bottle  it  should  be  emptied  out  on  paper, 
well  mixed  and  a  sufficient  amount  discarded  until  the  re- 
mainder is  small  enough  to  be  properly  handled  in  the  sampling 
bottle. 

Moisture.  A  one-gram  portion  of  the  well-mixed  60-mesh 
sample  is  weighed  into  an  empty  capsule  or  crucible  and  heated 
for  an  hour  at  105°  C.  in  a  constant-temperature  oven.  The 
capsule  is  then  removed  from  the  oven,  covered  and  cooled  in  a 
desiccator  over  sulphuric  acid.  The  loss  in  weight  times  100  is 
considered  as  the  percentage  of  moisture.  The  writer  prefers, 
for  moisture  determinations,  porcelain  capsules  about  1  inch 
high  by  1|  inches  in  diameter  at  the  top.  The  particular  kind 
used  has  been  obtained  from  The  Henry  Heil  Chemical  Co.,  of 
St.  Louis,  and  are  designated  as  porcelain-moisture  capsules  No. 

79 


80 


COAL 


2.  They  are  much  more  substantial  and  satisfactory  than  the 
ordinary  porcelain  crucible. 

The  lids  used  in  connection  with  the  capsules  are  stamped 
from  sheet  aluminium.  They  are  light  and  unbreakable  and  much 
more  convenient  to  handle  than  the  ordinary  covers  used  with 
porcelain  crucibles.  In  weighing  out  the  sample  at  the  beginning 
of  the  determination  the  lid  is  placed  upon  the  balance  pan  under 
the  empty  capsule  in  which  the  sample  is  weighed. 

The  oven  used  for  a  number  of  years  by  the  author  is  a  double- 


FIG.  5. — Moisture  Oven. 

walled  copper  cylinder,  see  Fig.  5;  the  space  between  the  outer 
and  inner  walls  being  filled  with  a  solution  of  glycerine  in  water, 
the  proportions  being  so  adjusted  that  the  boiling  solution  main- 
tains a  temperature  of  105°  C.  in  the  inner  chamber  of  the  oven. 
The  inner  cylinder  is  4|  inches  in  diameter  by  7  inches  long.  A 
removable  perforated  shelf  fits  into  this  inner  cylinder,  the  per- 
forations holding  six  capsules.  The  outer  cylinder  is  6J  inches 
in  diameter  by  8  inches  long.  Concentration  of  the  solution  is 


METHODS  OF  ANALYSIS  81 

prevented  by  means  of  a  condenser  fitted  on  to  the  top  of  the 
the  outer  cylinder.  Air  is  admitted  into  the  inner  chamber  of 
the  oven  through  a  coil  of  block  tin  or  copper  tubing,  which  passes 
around  the  inner  cylinder  and  is  surrounded  by  the  glycerine 
solution.  The  inner  end  of  this  tubing-  is  soldered  into  the  rear 
wall  of  the  inner  chamber;  the  outer  end  is  connected  to  a  flask 
containing  concentrated  sulphuric  acid.  During  a  determination 
a  current  of  air  dried  by  passing  through .  the  sulphuric  acid  is 
passed  through  the  copper  or  tin  tube  into  the  inner  chamber  of 
the  oven.  Passing  over  the  samples  it  takes  up  the  moisture  and 
escapes  through  a  small  opening  in  the  top  of  the  door  of  the  oven. 
The  air  is  passed  through  at  such  a  rate  that  a  volume  equal 
to  the  capacity  of  the  oven  passes  through  every  six  or  eight 
minutes.  Operating  a  moisture  oven  in  this  way  insures  a  uni- 
form condition  in  the  oven  irrespective  of  laboratory  humidity 
and  temperature  conditions  and  results  run  at  different  times 
are  strictly  comparable,  which  is  not  the  case  in  an  ordinary 
moisture  oven. 

The  use  of  sulphuric  acid  in  the  desiccator  in  which  the 
moisture  sample  is  cooled  gives  more  concordant  results  than 
where  calcium  chloride  is  used.  Experiments  show  that  if  the  dry 
sample  is  allowed  to  remain  over  calcium  chloride  for  any  con- 
siderable period  of  time  it  increases  in  weight  and  the  results  for 
moisture  are  accordingly  low.  To  avoid  the  danger  of  sulphuric 
acid,  in  the  desiccator,  splashing  up  on  the  bottom  of  the  cap- 
sule when  the  desiccator  is  carried  around  the  laboratory,  a  thin 
sheet  of  asbestos  paper  should  be  placed  below  the  capsule,  care 
being  taken  to  have  it  fit  loosely  enough  in  the  desiccator  to 
allow  free  circulation  of  air. 

The  cut  shows  9  turns  of  tubing,  however,  4  or  5  turns  are 
probably  just  as  efficient  and  are  less  expensive. 

Ash.  The  ash  is  determined  on  the  residue  of  coal  from  the 
moisture  determination.  The  capsule  containing  the  coal  is 
placed  in  a  muffle  furnace  and  slowly  heated  until  the  volatile 
matter  is  given  off.  This  slow  heating  avoids  coking  the  sample 
and  renders  it  easier  to  burn  to  ash.  After  the  volatile  matter 
is  expelled  the  temperature  of  the  muffle  is  raised  to  redness  and 
the  heating  is  continued  until  all  black  carbon  is  burned  out. 
The  capsule  is  then  removed  from  the  muffle  furnace,  cooled 
in  a  desiccator  and  weighed.  It  is  then  replaced  in  the  muffle 


82  COAL 

for  thirty  minutes,  again  cooled  and  re- weighed.  If  the  change 
in  weight  is  less  than  0.0005  gram  the  ash  is  considered  burned 
to  constant  weight.  If  the  variation  is  greater  than  this  the  ash 
is  again  ignited  for  30  minutes  and  again  cooled  and  re-weighed 
the  process  being  continued  until  the  difference  in  weight  between 
two  successive  ignitions  is  less  than  0.0005  gram.  In  the  case 
of  coals  high  in  iron,  ignition  to  constant  weight  is  sometimes 
difficult  on  account  of  small  variations  in  weight  due  to  oxidation 
and  reduction  of  the  compounds  of  iron.  The  amount  of  ash  as 
determined  represents  the  ignited  mineral  matter  in  the  coal. 

In  regular  routine  work  the  cooling  in  desiccators  may  be 
dispensed  with  and  the  capsules  cooled  on  clay  triangles  in  the 
open  air.  A  set  of  six  triangles  mounted  on  a  wood  base  is  very 
convenient  for  carrying .  the  capsules  from  the  furnace  to  the 
balance  and  from  the  balance  back  to  the  furnace.  This  arrange- 
ment is  lighter  and  easier  to  handle  than  desiccators  and  the  time 
required  for  cooling  is  much  less. 

The  capsules  cooled  in  air  weigh  about  0.0005  gram  more  than 
if  cooled  in  desiccators,  hence  the  ash  results  run  a  trifle  high,  but 
for  most  samples  the  difference  is  of  very  minor  importance  and 
the  saving  in  time  and  labor  considerable.  If  results  of  highest 
accuracy  are  required  the  cooling  should  be  done  in  desiccators. 

Volatile  matter.  A  one-gram  sample  of  the  fine  (60-mesh) 
coal  is  weighed  into  a  bright,  well-burnished  30-gram  platinum 
crucible  with  a  close  fitting  cover.  The  crucible  and  contents 
are  heated  upon  a  platinum  or  nichrome  triangle  for  7  minutes 
over  a  Bunsen  flame. 

The  crucible  and  residue  are  cooled  and  weighed,  the  loss  in 
weight  minus  the  weight  of  the  moisture  in  the  sample  determined 
at  105°  C.  times  100  equals  the  percentage  of  volatile  matter. 

With  artificial  gas  the  height  of  the  flame  should  be  18  to  20 
cm.  With  natural  gas  the  height  of  the  flame  should  be  about 
30  cm.  In  using  artificial  gas  the  bottom  of  the  crucible  should 
be  about  7  cm.  above  the  top  of  the  burner.  With  natural  gas 
the  bottom  of  the  crucible  should  be  about  12  cm.  above  the 
burner.  To  protect  the  crucible  from  air  currents  it  is  desirable 
to  enclose  the  flame  in  a  chimney.  A  cylindrical  chimney  15  cm. 
long  by  7  cm.  in  diameter,  notched  at  the  top  so  that  the  plat- 
inum triangle  is  about  3  cm.  below  the  top  of  the  chimney,  makes 
a  satisfactory  working  arrangement.  This  chimney  is  preferably 


METHODS  OF  ANALYSIS  83 

of  sheet-iron  lined  with  asbestos  but  a  fairly  satisfactory  chimney 
can  be  made  by  moistening  a  thick  sheet  of  asbestos  and  rolling 
it  into  a  cylinder.  This>  if  well  wrapped  with  wire  makes  a  fairly 
serviceable  chimney.  For  lignites  and  coals  containing  a  high 
percentage  of  moisture  the  method  should  be  modified  by  giving 
the  sample  a  preliminary  heating  at  a  low  temperature  for  several 
minutes  to  drive  out  the  moisture  in  order  to  avoid  mechanical 
losses  which  will  occur  if  such  a  sample  is  heated  over  the  full 
flame  of  the  burner  from  the  beginning.  This  preliminary  heating 
for  three  to  four  minutes  should  be  followed  by  the  regular  7- 
minute  application  of  the  full  flame,  after  which  the  sample  is 
cooled  and  weighed  as  in  the  regular  determination. 

The  higher  the  temperature  at  which  the  volatile  matter  is 
expelled  the  greater  is  the  percentage  of  volatile  matter  obtained. 
The  latest  data  on  this  subject  (Sept.,  1912)  is  by  Fieldner  and 
Hall l.  As  a  result  of  their  experiments  they  recommend  1000° 
C.  as  the  most  desirable  temperature  at  which  to  make  this  de- 
termination. Their  results  using  a  No.  4  Meker  burner  with 
natural  gas  compare  very  favorably  with  their  results  obtained 
by  heating  the  sample  in  an  electric  furnace. 

Fixed  Carbon.  The  fixed  carbon  is  the  difference  between  100 
and  the  sum  of  the  moisture,  ash  and  volatile  matter. 

Sulphur.     Sulphur  is  determined  by  either  of  two  methods: 

(a)  The  Eschka  method. 

(b)  The  determination  of  the  sulphur  in  the  washings  from 
the  calorimeter. 

The  two  methods  give  closely  agreeing  results  on  most  sam- 
ples. As  a  rule  the  determination  on  the  washings  from  the 
calorimeter  run  a  trifle  lower  than  by  the  Eschka  method  and 
where  the  exactness  of  the  sulphur  determination  is  of  more  than 
ordinary  importance  the  Eschka  method  should  be  used.  The 
details  of  the  methods  are  as  follows: 

Eschka  Method.  One  gram  of  the  sample  is  thoroughly 
mixed  in  a  30  c.c.  platinum  crucible  with  about  one  and  one-half 
grams  of  the  Eschka  mixture  (two  parts  light  calcined  magnesium 
oxide  plus  one  part  anhydrous  sodium  carbonate) ;  about  one-half 
gram  of  the  mixture  is  then  spread  on  top  as  a  cover. 

The  burning  is  done  over  grain  or  wood  alcohol,  gasoline  gas 
or  natural  gas,  experiments  having  shown  that  the  sulphur  con- 

1  Eighth  International  Congress  of  Applied  Chemistry,  Vol.  X,  p.  139. 


84  COAL 

tained  in  gasoline  gas  and  natural  gas  is  so  small  that  little  or 
none  of  it  is  taken  up  by  the  Eschka  mixture.  Ordinary  arti- 
ficial gas  is  so  high  in  sulphur  that  its  use  is  not  permissible,  as 
blanks  are  likely  to  be  large  and  variable  and  consequently  the 
correction  to  be  applied  is  uncertain.  At  the  beginning  the  flame 
is  kept  low  until  the  volatile  matter  is  burned  out.  This  requires 
from  15  to  30  minutes.  The  heat  is  then  increased  and  the  mix- 
ture stirred  occasionally  with  a  platinum  wire,  the  heating  being 
continued  till  all  traces  of  unburned  carbon  have  disappeared. 

The  mixture  in  the  crucible  is  then  transferred  to  a  200  c.c. 
beaker  and  digested  with  75  c.c.  of  water  for  at  least  30  minutes. 
The  solution  is  then  filtered  and  the  residue  washed  twice  with 
hot  water  by  decantation  and  then  washed  on  the  filter,  small 
portions  of  water  being  used  for  each  of  the  washings  until  the 
filtrate  amounts  to  200  c.c.  Bromine  water  in  excess  is  then 
added,  and  the  solution  made  slightly  acid  with  hydrochloric  acid. 
The  amounts  of  these  reagents  usually  added  are  4  c.c.  of  water 
saturated  with  bromine  and  3  c.c.  of  concentrated  hydrochloric 
acid. 

The  solution  is  heated  nearly  to  boiling  and  the  sulphur  pre- 
cipitated with  20  c.c.  of  a  hot  5  per  cent  solution  of  barium 
chloride,  slowly  added  from  a  pipette  during  constant  stirring. 
The  solution  and  precipitate  are  allowed  to  stand  at  a  temperature 
a  little  below  boiling  for  two  hours  or  longer  before  filtering. 
The  filtrate  from  the  barium  sulphate  is  tested  for  acidity,  with 
litmus  paper,  and  for  excess  of  barium  chloride  by  adding  a  few 
drops  of  dilute  sulphuric  acid  to  a  few  c.c.  of  the  filtrate  in  a  test 
tube.  The  preliminary  washing  of  the  precipitate  is  done  with 
hot  water  containing  1  c.c.  of  hydrochloric  acid  per  liter.  The 
final  washings  are  made  with  hot  water  alone  and  the  washing  is 
continued  until  the  washings  no  longer  react  for  chlorine  when 
tested  with  silver  nitrate. 

The  precipitate  is  ignited  in  a  porcelain  crucible.  The  filter 
and  precipitate  are  placed  in  the  crucible,  precipitate  uppermost, 
and  the  filter  folded  only  enough  to  prevent  loss  by  spattering. 
A  low  heat  is  used  until  the  paper  is  entirely  "  smoked  off."  The 
heat  is  then  raised  sufficiently  to  bring  the  precipitate  to  dull 
redness  and  the  heating  continued  for  a  few  minutes,  or  until  the 
carbon  is  burned  out.  The  crucible  and  precipitate  are  then  cooled 
and  weighed.  The  weight  of  barium  sulphate  less  the  blank 


METHODS  OF  ANALYSIS  85 

from  the  reagents,  times  0.137,  times  100,  equals  the  percentage  of 
sulphur  in  the  sample. 

Sulphur  in  the  calorimeter  washings.  The  determination 
of  the  sulphur  in  the  washings  from  the  calorimeter  is  as  follows: 
The  washings  are  slightly  acidulated  with  hydrochloric  acid  and 
filtered  from  the  residue  of  ash,  the  filtrate  is  heated  to  boiling 
and  the  sulphur  precipitated  as  in  the  Eschka  method. 

ULTIMATE    ANALYSIS 

The  ultimate  analysis  is  best  made  in  a  25-burner  combustion 
furnace.  The  details  of  the  train  and  description  of  the  method 
of  work  are  as  follows : 

The  purifying  train  through  which  the  air  and  oxygen  are 
passed  before  they  enter  the  combustion  tube  is  arranged  in  dupli- 
cate, one  part  for  air,  the  other  for  oxygen.  The  purifying  re- 
agents, arranged  in  the  order  named,  are  sulphuric  acid,  potas- 
sium hydroxide,  soda-lime  and  granular  calcium  chloride.  The 
combustion  tube  is  about  40  inches  long  and  about  f  inch 
internal  diameter.  The  tube  extends  beyond  each  end  of  the  fur- 
nace about  four  inches,  the  ends  of  the  tube  being  protected 
from  the  heat  of  the  furnace  by  closely  fitting  circular  shields 
of  asbestos.  The  rear  end  of  the  tube  (the  end  next  to  the  puri- 
fying train)  is  closed  with  a  rubber  stopper.  This  end  of  the  tube 
being  kept  cool  by  the  protection  of  the  circular  shield  and  by  the 
passage  of  cool  air  and  oxygen,  there  is  very  little  danger  of  vola- 
tile products  being  given  off  by  the  rubber.  The  other  end  of  the 
tube  is  closed  by  a  well-rolled  cork  of  specially  selected  quality, 
the  danger  from  over-heating  at  this  end  of  the  tube  being  too 
great  to  permit  of  the  use  of  the  more  convenient  rubber  stopper. 
This  end  of  the  tube  may  if  desired  be  drawn  out  so  that  the 
absorption  train  may  be  connected  to  it  direct  and  thereby  avoid 
the  danger  of  leakage  from  the  use  of  a  cork.  In  selecting  a  tube 
for  use  care  should  be  taken  to  avoid  the  heavy  walled  tubes  as 
the  thin  tubes  are  much  less  liable  to  breakage. 

The  rear  end  of  the  tube  for  10  inches  inside  the  furnace  is 
left  empty;  the  next  14  inches  is  filled  with  a  loose  layer  of  wire 
copper  oxide,  with  a  plug  of  acid-washed  and  ignited  asbestos 
at  either  end  to  hold  the  oxide  in  place.  The  copper  oxide  is  fol- 
lowed by  a  layer,  about  4  inches  long,  of  coarse  fused  lead  chro- 


86  COAL 

mate  to  stop  sulphur  products,  this  being  held  in  place  by  a  final 
plug  of  asbestos. 

The  absorption  train  is  as  follows:  The  water  is  absorbed  in 
a  six-inch  U-tube,  filled  with  granular  calcium  chloride;  the  car- 
bon dioxide  is  absorbed  by  potassium  hydroxide  in  an  ordinary 
Liebig  bulb,  to  which  is  attached  a  three-inch  U-tube  containing 
soda-lime  and  calcium  chloride,  the  bulb  and  U-tube  being 
weighed  together.  This  is  followed  by  a  final  guard  tube  filled 
with  calcium  chloride  and  soda-lime.  The  gases  formed  during 
combustion  are  drawn  through  the  train  by  suction,  a  Marriott 
bottle  being  used  to  secure  a  constant  suction  head. 

The  oxygen  used  is  kept  over  water  and  is  supplied  under 
small  pressure.  The  supply  of  oxygen  and  the  aspiration  during 
a  combustion  are  so  regulated  as  to  keep  the  difference  in  pressure 
between  the  inside  and  outside  of  the  tube  very  small,  the  pres- 
sure inward  being  slightly  greater.  This  reduces  the  danger  of 
leaks  to  a  minimum,  and,  if  by  chance  any  slight  leakage  does 
occur,  it  is  inward  rather  than  outward  and  the  effect  upon  the 
determination  is  small. 

Carbon  and  hydrogen.  Before  beginning  the  determination, 
the  apparatus  is  tested  for  leaks  by  starting  the  aspirator  and 
shutting  off  the  supply  of  air.  With  the  aspirator  on  full,  if  not 
more  than  four  or  five  bubbles  of  air  per  minute  pass  through 
the  potash  bulb,  the  connections  are  sufficiently  tight  to  proceed 
with  the  determination.  Air  is  then  admitted  to  the  purifying 
apparatus,  the  tube  heated  to  redness  throughout  and  1000  c.c. 
or  more  of  air  aspirated.  The  potash  bulb  and  drying  tube  are 
then  detached  and  weighed.  They  are  again  connected  and  500  c.c. 
of  oxygen  followed  by  1000  c.c.  of  air  aspirated  through  the  train. 

On  commencing  the  second  aspiration  the  burners  under  the 
rear  portion  of  the  tube  are  gradually  turned  down  and  finally 
entirely  out,  so  that  the  empty  portion  of  the  tube  into  which  the 
sample  for  analysis  is  to  be  inserted  becomes  nearly  or  quite  cool, 
by  the  time  the  aspiration  is  complete.  The  burners  under  the 
two-thirds  of  the  copper  oxide  next  to  the  lead  chromate  are 
kept  lighted  and  this  portion  of  the  oxide  kept  at  a  red  heat. 
After  aspiration  of  the  1000  c.c.  of  air,  the  potash  bulb  and  drying 
tube  are  detached  and  again  re  weighed.  If  the  gain  or  loss  in 
weight  is  less  than  five-tenths  milligram  the  apparatus  is  ready 
for  use. 


METHODS  OF  ANALYSIS  87 

The  absorption  apparatus  is  then  again  connected  and  0.2 
gram  of  the  well-mixed  sample  weighed  into  a  platinum  boat  and 
the  boat  and  sample  pushed  into  place  in  the  combustion  tube  as 
quickly  as  possible  and  slow  aspiration  of  the  train  started  at  the 
rate  of  one  or  two  bubbles  a  second  through  the  potash  bulbs  and 
a  mixture,  in  the  proportion  of  about  two  bubbles  of  oxygen  to  one 
of  air,  admitted  into  the  train  through  the  purifying  apparatus. 
The  burners  under  the  remaining  copper  oxide  and  behind  the  boat 
are  lighted  and  the  moisture  and  volatile  matter  gradually  driven 
off. 

This  part  of  the  operation  requires  very  careful  watching  and 
manipulation  to  secure  correct  results.  The  copper  oxide  must 
be  at  a  good  red  heat  or  the  combustion  of  the  hydrocarbons  is 
liable  to  be  incomplete.  If  the  evolution  of  the  hydrocarbons 
is  too  rapid  incomplete  combustion  or  absorption  also  results. 
Also  if  the  evolution  is  too  rapid  back  pressure  is  developed  in 
the  train  and  losses  are  almost  sure  to  occur,  either  from  mois- 
ture getting  back  into  the  tube  of  the  purifying  apparatus  or  from 
slight  leaks  in  the  train.  When  the  volatile  matter  is  expelled 
that  portion  of  the  tube  containing  the  boat  is  heated  to  redness, 
more  oxygen  is  admitted  into  the  train  and  the  fixed  carbon 
gradually  burned  off,  using  care  not  to  allow  the  combustion  to 
take  place  too  rapidly  or  fusion  of  the  ash  and  incomplete  com- 
bustion may  result. 

Oxygen  is  admitted  for  about  2  minutes  after  the  fixed 
carbon  is  burned  out,  which  may  be  seen  by  the  sudden  disap- 
pearance of  the  glow.  The  oxygen  is  then  turned  off  and  air 
aspirated  through  the  train,  the  burners  under  the  rear  portions 
of  the  tube  being  gradually  turned  down  and  out.  After  1000  c.c. 
have  been  aspirated  the  absorption  apparatus  is  detached  and 
weighed.  One-ninth  the  increase  in  the  weight  of  the  drying  tube 
equals  the  weight  of  the  hydrogen  and  three-elevenths  of  the 
increase  in  the  weight  of  the  potash  bulb  equals  the  weight  of  the 
carbon  from  the  sample. 

The  weight  of  the  hydrogen  and  of  the  carbon  in  grams  times 
5  times  100  equal  the  percentage  of  each  in  the  sample.  After  the 
completion  of  a  determination  the  platinum  boat  is  removed  from 
the  rear  of  the  combustion  tube  and  the  ash  examined  for  unburned 
carbon.  If  desired  the  ash  may  be  weighed  as  a  check  upon  the 
amount  determined  by  the  regular  method.  With  a  high  per- 


88  COAL 

centage  of  iron  in  the  ash  the  ultimate  ash  usually  runs  a  little 
higher  than  the  results  obtained  by  burning  out  a  gram  sample 
in  the  muffle  furnace  owing  probably  to  the  more  complete  oxida- 
tion of  the  iron  in  the  sample  burned  in  the  combustion  train. 
To  make  another  determination,  the  absorption  apparatus  is 
again  connected  to  the  train  and  another  sample  weighed  into 
the  platinum  boat  and  inserted  into  the  rear  of  the  combustion 
tube. 

In  weighing  the  sample,  the  work  should  be  done  as  rapidly 
as  possible  and  as  soon  as  weighed  the  boat  and  sample  should  be 
placed  in  a  glass  weighing  tube  which  should  be  securely  stop- 
pered to  prevent  moisture  losses.  The  sample  is  carried  from  the 
balance  room  to  the  combustion  train  in  the  closed  weighing 
tube.  The  transfer  from  the  weighing  tube  to  the  combustion 
tube  should  be  made  quickly  and  the  connections  of  the  com- 
bustion tube  fitted  up  without  undue  loss  of  time. 

Aspiration  to  constant  weight  is  unnecessary  between  deter- 
minations which  follow  one  another  immediately,  but  cannot 
safely  be  neglected  if  the  train  is  allowed  to  stand  for  several 
hours.  At  the  beginning  of  a  series  of  determinations  aspiration 
to  constant  weight  is  always  necessary.  Also  aspiration  to  con- 
stant weight  is  necessary  after  the  re-filling  of  the  potash  bulbs 
or  if  a  new  bulb  is  substituted.  The  potash  bulbs  hold  sufficient 
potash  for  four  or  five  determinations,  after  which  the  solution 
should  be  replaced  by  fresh  reagent.  The  potash  solution 
should  have  a  specific  gravity  of  about  1.27,  which  corresponds 
to  about  a  30  per  cent  solution.  The  stock  solution  should  be 
treated  with  a  few  drops  of  permanganate  solution  to  oxidize 
any  ferrous  iron  or  other  oxidizable  compounds  present,  which 
if  not  oxidized,  interfere  with  the  aspiration  of  the  bulb  to  constant 
weight. 

NITROGEN 

One  gram  of  the  finely  pulverized  coal  is  digested  with  30  c.c. 
of  concentrated  sulphuric  acid  and  0.6  gram  of  metallic  mercury 
until  the  carbon  is  completely  oxidized  and  the  liquid  is  nearly 
colorless.  The  digestion  should  be  continued  for  at  least  an  hour 
after  the  solution  has  reached  the  straw  color  stage.  Crystals 
of  potassium  permanganate  are  then  added,  a  few  at  a  time,  until 
a  permanent  green  color  remains.  After  cooling,  the  solution  is 


METHODS  OF  ANALYSIS  89 

diluted  to  about  300  c.c.  with  cold  water.  It  is  then  transferred 
to  a  750  c.c.  distillation  flask.  The  excess  of  mercury  is  precipi- 
tated by  adding  25  c.c.  of  potassium  sulphide  (E^S)  solution 
(40  grams  of  K2S  per  liter).  About  one  gram  of  granular  zinc 
is  added  to  prevent  bumping.  Enough  saturated  sodium  hydrox- 
ide (NaOH)  solution  (usually  about  80  c.c.)  is  added  to  make  the 
solution  distinctly  alkaline,  the  soda  being  added  carefully  so 
as  to  run  down  the  side  of  the  flask  and  not  mix  with  the  acid 
solution.  The  flask  is  then  connected  to  a  condenser,  the  contents 
mixed  by  shaking  and  then  heated  over  a  Bunsen  burner  until 
about  200  c.c.  of  distillate  have  been  obtained.  The  distillate  is 
collected  in  a  receiving  flask  containing  10  c.c.  of  standard  sul- 
phuric acid  solution  (1  c.c.  =0.005  gram  of  nitrogen)  to  which 
cochineal  indicator  in  amount  sufficient  for  titration  has  been 
added.  The  end  of  the  tube  carrying  the  distillate  should  dip 
beneath  the  surface  of  the  acid  at  all  times.  The  distillate  is 
then  titrated  with  standard  ammonia  solution  (20  c.c.  of  ammo- 
nia solution  =  10  c.c.  of  sulphuric  acid  solution  =  0.05  gram  of 
nitrogen) .  If  trouble  is  experienced  from  frothing  during  distilla- 
tion it  may  be  prevented  by  the  addition  of  a  small  piece  of 
paraffin  to  the  solution  before  distillation. 

A  convenient  method  of  adding  the  0.6  gram  of  mercury  is 
to  measure  it  rather  than  to  weigh  it.  This  can  readily  be  done 
by  partially  filling  up  the  opening  in  a  glass  stop-cock  so  that 
when  the  cock  is  turned  it  carries  and  delivers  a  drop  of  mercury. 
Such  an  apparatus  correctly  calibrated  will  deliver  practically 
the  same  amount  each  time,  and  the  addition  of  the  mercury  can 
be  made  in  one-tenth  the  time  required  to  weigh  out  the  desired 
amount. 

For  further  details  of  the  Kjeldahl  process,  see  Bulletin  107 
(Revised)  U.  S,  Department  of  Agriculture,  Bureau  of  Chemistry. 

PHOSPHORUS 

In  the  determination  of  phosphorus  5  to  10  grams  of  sample 
are  burned  to  ash  in  the  muffle  furnace.  The  ash  is  mixed  in  a 
platinum  crucible  with  four  to  six  times  its  weight  of  sodium 
carbonate  and  about  0.2  gram  of  sodium  nitrate  and  is  fused 
over  the  blast  lamp.  The  fused  mass  is  dissolved  in  water,  acidi- 
fied and  evaporated  to  dry  ness.  The  residue  is  taken  up  in 


90  COAL 

hydrochloric  acid  and  the  phosphorus  determined  in  the  usual 
way  either  by  weighing  the  yellow  precipitate  or  titrating  it  with 
permanganate  or  standard  alkali.  For  details  of  phosphorus 
determinations  see  Lord's  "  Notes  on  Metallurgy  "  or  other  texts 
on  metallurgical  analysis. 

OXYGEN 

No  reliable  method  is  known  for  the  direct  determination  of 
the  oxygen  in  coal  and  it  is,  therefore,  determined  by  difference. 
The  sum  of  the  percentages  of  hydrogen,  carbon,  nitrogen,  sul- 
phur and  ash  is  subtracted  from  100  and  the  remainder  is  called 
oxygen.  This  result  is  always  inaccurate  in  that  it  does  not 
represent  the  true  amount  of  oxygen  in  the  coal.  The  amount  of 
the  inaccuracy  increases  with  the  percentage  of  the  ash  and  sul- 
phur. The  effects  of  ash  and  sulphur  upon  the  value  obtained  for 
oxygen  have  been  discussed  elsewhere  and  do  not  need  repetition 
at  this  point. 


CHAPTER  V 
DETERMINING  THE  CALORIFIC  VALUE 

THE  establishment  and  use  of  specifications  for  the  purchase 
and  sale  of  coal  based  upon  the  heating  value  require  the  actual 
determination  of  the  heating  value  of  the  sample  or  samples  which 
are  used  as  the  basis  of  settlement,  and  in  analyzing  such  sam- 
ples the  chemist  is  expected  and  required  to  make  this  determina- 
tion along  with  the  determination  of  moisture,  ash  and  sulphur. 
At  present  some  form  of  pressure  calorimeter,  in  which  the  sam- 
ple is  burned  in  a  steel  bomb  under  15  to  25  atmospheres  pres- 
sure of  oxygen,  is  generally  regarded  as  the  standard  type  of 
calorimeter,  and  specifications  for  the  purchase  of  coal  frequently 
specify  that  the  heating  value  shall  be  determined  in  a  bomb 
calorimeter.  Some  of  the  commoner  types  of  this  form  of  calo- 
rimeter are :  the  Mahler,  the  Atwater,  the  Emerson,  the  Williams, 
and  the  Kroecker. 

The  details  of  the  method  of  making  a  determination  and  the 
calculation  of  the  results  are  as  follows:  This  description  is  based 
primarily  upon  the  use  of  a  Mahler  calorimeter  but  is  applicable 
with  minor  modifications  to  any  of  the  other  calorimeters  men- 
tioned. About  2  grams  of  the  60-mesh  sample  are  pressed  into 
a  small  briquet  by  means  of  a  small  screw  press  and  mold.  The 
press  used  by  the  writer  is  the  iron  frame  of  a  2-quart  tincture 
press  manufactured  by  the  Enterprise  Manufacturing  Company 
of  Philadelphia,  Pa.  After  removal  from  the  mold  the  briquet 
is  broken  into  smaller  portions  and  about  1  gram  accurately 
weighed  and  placed  in  the  platinum  combustion  tray  which  is 
covered  with  a  thin  disc  of  asbestos  paper  that  has  been  washed 
with  hydrochloric  acid  and  ignited  in  a  muffle  furnace.  The  tray 
is  then  attached  to  one  of  the  platinum  terminals  fitted  to  the  lid 
and  the  terminals  are  connected  by  a  piece  of  iron  wire  (platinum 
wire  should  be  used  when  the  bomb  is  platinum  lined)  about  10 
centimeters  long  and  formed  into  a  spiral.  The  ends  of  the  wire 

91 


92  COAL 

are  attached  to  the  clean  platinum  terminals,  by  wrapping  the 
wire  tightly  around  them.  The  spiral  is  bent  down  so  that  it 
touches  the  coal  sample  in  the  tray.  The  lid  is  placed  on  the 
bomb  and  screwed  down  tightly  against  the  lead  gasket.  Oxygen 
under  pressure  is  admitted  gradually  into  the  bomb  through 
the  valve  stem  until  the  manometer  recording  the  pressure 
reads  18  to  20  atmospheres.  The  needle  valve  is  then  closed. 
Very  little  force  should  be  used  in  closing  it  and  extra  pressure 
should  be  avoided. 

The  bomb  filled  with  oxygen  is  placed  in  the  brass  bucket 
Containing  from  2400  to  2500  grams  of  distilled  water,  the  bucket 
having  been  previously  placed  in  the  insulated  jacket.  The 
stirring  apparatus  is  then  adjusted  so  that  it  touches  neither  the 
bucket  nor  bomb  and  works  freely.  The  thermometer  for  record- 
ing the  temperature  rise  is  clamped  into  position  and  so  adjusted 
that  the  lower  end  of  the  mercury  bulb  is  about  5  centimeters 
above  the  bottom  of  the  bucket.  The  outside  terminals  of  the 
bomb  are  connected  with  wires  leading  to  the  switch.  The  stirrer 
is  then  set  in  motion  and  the  readings  of  the  thermometer  taken 
by  means  of  a  telescope  attached  to  a  cathetometer.  The  ther- 
mometer is  graduated  to  -^th  degree  Centigrade  and  the  readings 
can  be  interpolated  to  thousandths  of  a  degree.  The  stirring 
should  be  continued  at  a  uniform  rate  throughout  the  determina- 
tion and  should  be  sufficiently  rapid  to  insure  thorough  mixing. 
Preliminary  readings  are  taken  at  intervals  of  one  minute  each 
for  about  five  minutes  or  until  the  rate  of  change  per  minute  is 
nearly  uniform  and  a  definite  rate  is  established.  The  switch  is 
then  closed  and  the  current  turned  on  for  about  one-half  second. 
The  ignition  of  the  sample  is  followed  by  a  very  rapid  increase 
in  temperature  and  the  first  two  readings  after  combustion  are 
taken  one-half  minute  apart.  Other  readings  are  then  taken  at 
minute  intervals.  The  temperature  usually  reaches  a  maximum 
in  three  or  four  minutes  but  the  series  of  readings  is  continued 
until  a  uniform  final  rate  has  been  established.  Not  less  than 
five  and  sometimes  as  many  as  seven  or  eight  readings  are 
required  to  determine  the  final  rate. 

The  calculations  involved  and  corrections  applied  are  shown 
by  a  typical  determination  on  p.  93. 

The  readings  from  7-50  to  7-54  are  the  readings  of  the  pre- 
liminary period.  The  increase  in  temperature  during  this  time 


DETERMINING   THE  CALORIFIC   VALUE 


93 


FORM  FOR  CALORIMETER  DETERMINATIONS 


DEPARTMENT  OF  METALLURGY, 

OHIO  STATE  UNIVERSITY. 
SAMPLE  No.  5160 

Wet  and  dry  bulbs  =  14-22°  C.  Coal  = 

Jacket  water  =21°  C. 

Room  temperature  =       22°  C. 

Time.  Readings  °  C.  Observed  final  temperature 

' '        initial  ' ' 


temperature  rise 
Radiation  correction 
Calibration  correction 
Stem  correction    .  .  . 

Corrected  temperature  dif. 
Water  equivalent  1° 


Date— 5-24-1912. 
1.0018  gms. 


7-50 

19 

.318) 

51 

19 

.326 

52 

19 

.334  \  =+0 

0075 

53 

19 

.340 

54 

19.  348  J   +0 

0075 

+0.0026 

1 

20 

.2     +0 

0030 

+0 

0001 

55 

21 

.40    -0 

0028 

-0 

0035 

56 

21 

.700    -0 

0043 

-0 

0043 

57 

21 

.746    -0 

0043 

-0.0043 

-0 

.0043 

58 

21 

.744 

59 

21 

.740 

-0 

0094 

60 

21 

.736 

1 

21 

.734 

•  =-0 

.0043 

2 

21 

.728 

3 

21 

.722 

4 

21 

.718 

21.744 
19.348 


Calories  of  heat  developed 
Corrections 


2.396 

=    +0.0094 
=    -0.006 
=    +0.0014 

=   2.4008 
2875 

5750.0 
1150.0 

00.0 

00.0 
2.3 

=  6902.3 
-  101.6 


Heat  from  sample  =6800.7 

Correction  for  excess  sample 

over  1  gram  =     12.2 


Calorific  value  of  coal 


=  6788.5 


Wire  fuse  =  10  cm. 

unburned=2  cm. 

"      "      burned      =8  cm.  (1  cm.  =2.4  cal.)    =    19.2  cal. 
Titer,  23.8  to  31.6      =7.8  cc.  (1  cc.=5  cal.)        =39.0" 
Sulphur  in  coal  3.34  per  cent  (.01  gm.  =  13  cal.)  =   43 . 4    ' 


Total  correction 


=  101.6    ' 

Thermometer  used,  No.  5764  Position  5  c.m. 

Scale  reading  18.3.  Stem  temperature  22°  C 

Atmospheres  oxygen  used  =  18  Valve — tight. 

At  19°  add  4.5  c.c.  of  water  to  obtain  2400  gms. 

(Signed)  C.H.Y.— 
Checked  E.S.D.— 

is  19.318  to  19.348  =  0.030  or  0.0075  degree  per  minute.  The 
switch  was  closed  and  the  combustion  started  at  7-54,  the  maxi- 
mum observed  temperature  being  at  7-57.  From  7-58  to  7-64 


94  COAL 

the  rate  of  loss  is  quite  regular.  Inspection  shows  this  loss  to  be 
about  0.004  degree  per  minute.  The  temperature  at  7-58  is  taken 
as  the  end  of  the  combustion  period  since  it  is  the  first  reading 
that  falls  in  line  with  this  rate  of  loss.  The  loss  during  the  six 
minutes  following  the  combustion  period  is  21.744—21.718  = 
0.026  or  0.0043  degree  per  minute.  The  observed  temperature 
increase  is  the  difference  between  the  temperature  at  the  begin- 
ning and  end  of  the  combustion  period  or  21.744-19.348  =  2.396°. 
The  total  change  in  the  rate  of  gain  or  loss  in  the  system  cor- 
responding to  2.39°  increase  of  temperature  is  from  a  rate  of 
+0.0075  to  a  rate  of  -0.0043,  a  total  change  of  0.0118°.  A 
change  of  rate  of  0.0118  with  a  change  of  temperature  of  2.4° 
(counting  to  the  nearest  0.1°)  is  equivalent  to  a  change  of  rate  of 
approximately  0.0005°  for  each  0.1°  temperature  change,  from 
which  the  rate  of  gain  or  loss  at  the  different  readings  can  be 
obtained.  The  rate  of  gain  or  loss  at  the  58th  minute  is  the 
final  rate  — 0.0043.  The  temperatures  at  the  57th  and  56th  min- 
utes are  within  0.1°  of  the  temperature  at  the  58th  minute  and 
the  rate  of  loss  is  the  same  as  that  at  the  58th  minute.  The 
temperature  at  the  55th  minute  is  approximately  0.3°  lower  and 
the  rate  of  loss  is  accordingly  less  by  0.3X0.0005°  =  0.0015  or  the 
rate  of  change  at  the  55th  minute  is  -0.0043+0.0015=  -0.0028°. 
At  54  J  minutes  the  temperature  to  the  nearest  0.1°  is  0.9°  higher 
than  at  the  54th  minute.  The  rate  of  change  corresponding  to 
0.9°  is  9X0.0005  =  0.0045.  Subtracting  this  change  from  the  rate 
of  change  at  the  54th  minute  =  +0.0030.  The  actual  tem- 
perature gain  or  loss  for  each  of  the  different  intervals  is  found 
by  adding  the  rates  at  the  beginning  and  end  of  the  interval  and 
dividing  by  2  if  a  minute  interval  or  by  4  if  a  half-minute  inter- 
val. The  sum  of  the  rates  at  the  beginning  and  end  of  the  inter- 
val from  54  to  54J  is  +0.0075+ (+0.0030)  = +0.0105.  This 
divided  by  4  and  carrying  the  result  to  the  nearest  fourth 
decimal  =+0.0026°,  the  temperature  gain  during  the  interval. 
For  the  interval  54|  to  55,  +0.0030+ (-0.0028)  =0.0002.  This 
divided  by  4  gives  0.00005  or  to  the  nearest  fourth  decimal 
=  +0.0001°.  For  the  minute  interval  55  to  56,  -0.0028+ 
(-0.0043)  =  -0.0071.  This  divided  by  2=  -0.0035°.  The  losses 
in  the  other  intervals  are  obtained  in  a  like  manner.  Adding 
together  the  different  gains  and  losses  the  total  loss  is  found  to 
be  0.0094,  from  which  the  radiation  correction  =  +0.0094°.  The 


DETERMINING   THE  CALORIFIC   VALUE  95 

calibration  correction  for  the  thermometer  used=  —0.0060°.  The 
stem  correction  =  +0.0014°.  The  corrected  temperature  difference 
=  2.4008°.  The  water  equivalent  of  the  calorimeter  system  is 
2875  calories.  Multiplying  the  corrected  temperature  change  by 
this  water  equivalent  (i.e.,  by  the  number  of  calories  necessary 
to  cause  a  rise  of  1°  of  temperature),  the  total  heat  developed 
during  combustion  is  2.4008X2875  =  6902.3. 

Corrections.  The  heat  from  the  burning  of  the  wire  fuse  is 
found  by  multiplying  the  weight  of  wire  taken  by  its  calorific 
value  (1600  calories  per  gram  =  2.4  calories  for  1  cm.).  8.0  cm.X 
2.4  =19.2  calories.  The  acidity  of  the  bomb  liquor  after  com- 
bustion is  found  by  titrating  it  with  a  standard  ammonia  of  such 
strength  (0.0059  grams  of  ammonia  per  c.c.,  see  acidity  correc- 
tions) that  one  c.c.  corresponds  to  a  heat  correction  of  five  calo- 
ries, assuming  the  acidity  to  be  entirely  due  to  nitric  acid,  from 
which  7.8  times  5  equals  39  calories,  the  correction  due  to  the 
formation  of  nitric  acid. 

A  large  part  of  the  acidity  in  high  sulphur  coal  is,  however 
due  to  sulphuric  acid,  and  the  heat  correction  for  acid  formed, 
considering  it  all  as  nitric  acid,  is  therefore  incomplete,  a  further 
correction  of  13  calories  for  each  0.01  gram  of  sulphur  present 
being  required.  (See  acidity  corrections.)  3.34  per  cent  sul- 
phur in  the  sample  is  0.0334  gram  sulphur  on  a  one  gram  sample 
taken.  Therefore,  the  correction  is  3.34X13  =  43.4  calories. 

The  total  of  these  corrections  is  101.6  calories.  6902.3,  the 
total  heat  developed,  less  this  correction  of  101.6  gives  6800.7 
calories  of  heat  from  the  combustion  of  the  coal.  These  6800.7 
calories  are  developed  by  1.0018  grams  of  sample.  The  value 
per  gram  is  therefore  6800.7  divided  by  1.0018.  The  amount  of 
sample  taken  is  so  near  one  gram  that  this  correction  can  be 
approximated  as  .68  of  a  calorie  for  0.0001  gram  of  coal.  For 
0.0018  the  correction  is  accordingly  18X0.68  =  12.2.  Making 
this  correction  gives  6788.5  as  the  calorific  value  of  the  coal. 

The  foregoing  description  of  the  calculations  makes  them 
appear  more  difficult  and  troublesome  than  they  really  are,  as 
practically  all  the  corrections  can  be  made  mentally,  and  the 
radiation  corrections  can  be  determined  very  readily  if  the  cal- 
culator is  familiar  with  the  routine  of  the  determination.  The 
use  of  .printed  blank  forms  saves  time  and  insures  regularity 
and  completeness  in  the  records. 


96  COAL 

SPECIAL  NOTES  ON  CALORIFIC  DETERMINATION 

Complete  combustion  of  the  sample.  To  insure  complete 
combustion  from  three  to  five  times  the  theoretical  amount  of 
oxygen  required  should  be  used  which  for  a  one-gram  sample 
of  coal  is  equivalent  to  approximately  from  9  to  15  grams  of  oxy- 
gen. In  a  bomb  of  the  Mahler  type  with  a  capactiy  of  600  c.c., 
the  author  has  found  it  unsafe  to  use  less  than  15  atmospheres 
pressure  of  oxygen  which  corresponds  to  about  11  grams  of  oxy- 
gen and  in  ordinary  work  18  to  20  atmospheres  corresponding  to 
about  15  grams  of  oxygen  are  preferable.  The  complete  ignition 
of  the  briquetted  sample  is  more  certain  if  the  briquet  is  not 
made  too  hard  and  is  broken  up  into  a  number  of  pieces.  The 
fine  sample  can  be  weighed  direct  and  the  combustion  made  upon 
the  coal  in  this  condition  if  care  is  used  in  admitting  the  oxygen 
to  the  calorimeter  not  to  blow  any  of  the  fine  coal  out  of  the  tray. 
On  account  of  this  danger  of  blowing  out  fine  coal  the  author 
prefers  briquetting  most  samples.  Anthracite  coal  and  coke  will 
not  briquet  readily  and  require  to  be  run  in  powdered  form. 
The  use  of  a  disc  of  ignited  asbestos  on  the  tray  to  lessen  the 
rate  of  conduction  of  heat  during  combustion  is  a  decided  ad- 
vantage in  securing  complete  combustion  of  cokes  and  anthracites 
which  are  much  more  difficult  to  burn  than  the  ordinary  bitu- 
minous coals. 

Preventing  leakage  of  valve.  By  use,  the  valve  through 
which  the  oxygen  is  admitted  into  the  calorimeter  soon  becomes 
corroded  from  the  action  of  the  acid  fumes  and  rusted  through  the 
action  of  moisture  and  air.  In  this  condition  it  is  extremely 
difficult  to  prevent  considerable  leakage  of  oxygen.  This  leakage 
may  be  prevented  and  the  valve  made  to  fit  tight  by  cutting  a 
thin  washer  of  lead  about  one-thirty-second  inch  in  thickness  and 
fitting  into  the  valve,  using  care  in  its  insertion  not  to  get  it  in 
crosswise  and  thereby  close  the  opening  into  the  bomb.  A  very 
efficient  way  to  insert  it  is  as  follows:  Hold  the  valve  stem, 
valve-end  up  and  slip  the  washer  over  the  tip  of  the  needle. 
Then  with  the  stem  in  this  vertical  position  screw  the  lid  on  to 
the  stem  carefully  till  the  washer  is  pressed  into  place.  Very 
slight  pressure  is  required  to  close  the  valve  when  fitted  in  this 
way  and  extra  pressure  is  to  be  avoided  as  tending  to  force  lead 
into  the  needle  opening,  which  may  be  entirely  closed  and  will  in 


DETERMINING  THE  CALORIFIC   VALUE  97 

this  event  require  drilling  out  before  the  bomb  can  be  used 
again. 

Leakage  around  the  lid.  As  a  rule  little  trouble  is  experienced 
from  leakage  around  the  lid  if  the  lead  gasket  is  kept  smooth. 
Moistening  the  gasket  with  a  drop  of  water  before  putting  on  the 
lid  considerably  lessens  the  danger  of  leakage.  The  film  of  water 
between  the  gasket  and  the  lid  of  the  bomb  appears  to  be  of  con- 
siderable advantage  in  securing  a  gas-tight  joint. 

Water  surrounding  the  bomb.  In  the  regular  routine  deter- 
minations the  amount  of  water  used  is  more  conveniently  meas- 
ured than  weighed.  For  this  purpose  the  author  uses  a  Florence 
flask  holding  about  2400  c.c.  of  water  when  filled  to  the  middle 
of  the  neck.  The  number  of  grams  of  water  that  it  delivers  is 
determined  by  filling  it  to  a  fixed  mark  and  weighing  at  a  definite 
observed  temperature.  The  flask  is  then  emptied  and  allowed  to 
drain  15  seconds  and  again  re-weighed,  an  allowance  of  2.4  grams 
being  made  for  the  effect  of  the  buoyancy  of  the  air  displaced  by 
this  amount  of  water.  The  difference  in  weight  is  the  number  of 
grams  of  water  the  flask  delivers  at  this  temperature.  A  table 
is  then  prepared  giving  for  different  temperatures  the  number 
of  c.c.  of  water  which  must  be  added  to  the  water  inside  of  the 
flask  to  obtain  2400  grams. 

The  diameter  of  the  necks  of  the  flasks  used  is  from  1 J  to  If 
inches.  With  this  size  of  neck  and  a  uniform  time  of  15  seconds 
for  drainage,  the  amount  of  water  can  easily  be  measured  to  an 
accuracy  of  1  c.c.  and  the  maximum  errors  of  measurement  do 
not  affect  the  calorific  value  obtained  over  two  or  three  calories. 
The  time  required  for  measuring  is  less  than  that  required  for 
weighing  and  does  not  involve  the  continued  use  of  an  expen- 
sive balance  and  set  of  weights. 

An  example  of  the  method  of  calibration  is  as  follows: 

Weight  of  flask  filled  with  water  to  a  definite  mark  =  2842.5  grams 
WTeight  of  empty  flask  after  draining  15  seconds      =   450.5      ll 


Difference  =  2392.0  " 

Corrections  to  weights  =    +  .6  " 

Corrections  for  buoyancy  of  air  =    +2.4  " 

Total  weight  of  water  delivered  =  2395.0  ' l 

Temperature  of  water  =  20°  C.     For  small  corrections  1  c.c. 


98  COAL 

of  water  may  be  taken  as  equal  to  one  gram  and  at  the  tempera- 
ture of  20°  C.  the  amount  of  water  to  be  added  to  the  flask  in 
order  that  it  may  deliver  2400  grams  is  5  c.c.  The  amounts  for 
other  temperatures  based  on  the  specific  gravity  of  water  at  the 
different  temperatures  are  obtained  as  follows: 

The  volume  of  the  flask  in  cubic  centimeters  =  2395,  divided 

2395 

by  the  specific  gravity  of  water  at  20°  C.  is  -        -  =2399.2. 

•  0.99823 

The  density  of  water  for  the  range  covered  by  ordinary  calori- 
metric  work  are  as  follows: 

Degrees  C.          Density.  Degrees  C.  Density. 


8° 

_ 

0.99988 

20° 

— 

0.99823 

10° 

= 

0.99973 

.  22° 

= 

0.99780 

12° 

= 

0.99953 

24° 

= 

0.99732 

14° 

= 

0.99928 

26° 

= 

0.99680 

16° 

= 

0.99898 

28° 

= 

0.99626 

18° 

= 

0.99863 

30° 

= 

0.99567 

The  weight  of  the  water  which  the  flask  will  deliver  when 
filled  to  the  mark  at  any  temperature  (i)  =  the  volume  of  the 
flask,  (2399.2)  times  the  density  of  the  water  at  temperature  (t). 
The  amount  of  water  to  be  added  at  any  given  temperature  when 
the  flask  is  filled  to  the  mark  is  2400  minus  what  the  flask  holds 
at  that  temperature.  At  10  degrees  this  particular  flask  holds 
2399.2X0.99973  =  2398.6.  Hence  the  correction  to  be  added 
=  2400  —  2398.6  =  1.4  grams  or  1.4  c.c.  Such  a  table  of  correc- 
tions once  prepared  is  pasted  on  the  side  of  the  flask  and  the 
proper  amount  to  add  for  any  particular  determination  readily 
determined. 

Temperature  conditions.  More  satisfactory  rates  of  gain 
or  loss  during  a  determination  are  secured  if  the  temperature 
differences  between  the  air  of  the  laboratory  and  that  of  the  water 
inside  the  inner  bucket  and  in  the  outer  insulating  jacket  are 
kept  small.  The  author's  practice  is  to  keep  the  temperature 
of  the  water  in  the  outer  jacket  within  a  few  degrees  of  room 
temperature.  The  water  to  be  used  in  the  inner  bucket  is  cooled 
till  its  temperature  is  about  two  to  three  degrees  lower  than  that 
of  the  water  in  the  outer  jacket,  care  being  taken  that  this  tem- 
perature is  not  too  near  the  dew-point.  In  warm,  damp  weather 
to  avoid  this  danger,  the  water  in  the  outer  jacket  is  kept  several 
degrees  above  room  temperature. 


DETERMINING  THE  CALORIFIC  VALUE          99 

With  these  temperature  relations,  the  greater  rate  of  change 
during  a  determination  is  before  the  combustion,  and  the  rate 
of  change  after  the  combustion  period  is  small.  The  larger  the 
rate  of  change  the  larger  is  the  possible  error.  The  effects  of  the 
larger  rate  before  the  combustion  period  are,  after  the  first  min- 
ute, practically  eliminated.  By  the  end  of  the  first  minute  most 
of  the  total  temperature  rise  has  occurred  and  the  rate  of  change 
during  the  other  minutes  of  the  combustion  period  approxi- 
mates in  value  the  final  rate.  With  the  final  rate  small  the  total 
corrections  are  correspondingly  small  and  errors  from  this  source 
are  reduced  to  a  minimum. 

CORRECTIONS  TO  BE  APPLIED 

Correction  for  nitric  acid.  The  data  and  calculation  of  the 
correction  are  as  follows:  In  burning  the  sample  in  the  bomb 
calorimeter,  under  pressure,  a  portion  of  the  nitrogen  in  the  fuel 
and  perhaps  is  burned  of  the  nitrogen  in  the  small  amount  of  air 
in  the  bomb  a  portion  to  N20s  aqua  while  in  combustion  of  fuel 
under  a  boiler  the  nitrogen  either  escapes  as  free  nitrogen  or 
burns  to  gaseous  N2O5  and  passes  off  in  the  flue  gases.  The  heat 
of  formation  of  N20s  aqua  is  approximately  1020  calories  per 
gram  of  nitrogen.  The  heat  of  liberation  of  the  nitrogen,  as  free 
nitrogen,  from  the  coal  is  not  definitely  known  but  is  presumably 
not  far  from  0.  The  heat  of  the  formation  of  gaseous  N2Os  from 
nitrogen  and  oxygen  is  approximately  —  36  calories  per  gram  of 
nitrogen.  In  either  case  the  heat  change  per  gram  of  nitrogen 
is  small  and  in  correcting  for  the  amount  of  nitric  acid  in  the 
bomb,  the  heat  of  formation  of  N2Os  aqua  is  usually  taken  as 
the  nitric  acid  correction.  The  reaction  for  neutralization  of 
nitric  acid  by  an  alkali  is  as  follows: 

2HN03+2NH4OH  =  2NH4N03+H2O, 

from  which  it  follows  that  14  parts  by  weight  of  nitrogen  as 
nitric  acid  equal  in  neutralizing  value  17  parts  by  weight  of 
ammonia  (NHs).  A  convenient  strength  for  the  titrating  alkali 
is  one  cubic  centimeter  equivalent  to  5  calories  of  heat.  Since 
1020  calories  are  produced  by  the  combustion  of  one  gram 


100  COAL 

of  nitrogen  then  5  calories  are  produced  by  the  combustion  of 

5 

— —  gram  =  0.0049  gram;    0.0049  gram  of  nitrogen  as  nitric  acid 

requires  HX  0.0049  gram  of  ammonia  for  neutralization  =  0.00595 
gram  of  ammonia  per  cubic  centimeter  or  5.95  grams  per  liter. 

Correction  for  sulphuric  acid.  Any  sulphuric  acid  present  is 
titrated  with  nitric  acid  and  its  heat  of  formation  is  partially 
allowed  for  by  considering  it  as  nitric  acid.  The  data  for  deter- 
mining the  amount  of  correction  necessary  and  the  amount  which 
is  allowed  for  by  considering  it  as  nitric  acid  are  as  follows:  The 
heat  of  formation  of  aqueous  sulphuric  acid  in  the  calorimeter 
is  approximately  4450  calorics  per  gram  of  sulphur.  In  ordinary 
combustion  in  air  the  sulphur  is  burned  to  sulphur  dioxide,  the 
heat  of  formation  of  which  is  approximately  2250  calories  per 
gram  of  sulphur. 

The  excess  heat  due  to  the  formation  of  sulphuric  acid  in 
the  bomb  is  therefore  4450  —  2250  =  2200  calories  per  gram  of 
sulphur.  In  neutralizing  with  ammonia  the  reaction  for  sul- 
phuric acid  is  as  follows:  H2SO4+2NH4OH  =  (NH4)2SO4+H2O, 
or  in  titrating  H2SO4  =  2HN03  =  2NH4OH.  Expressed  by  weight 
32  parts  of  sulphur  as  sulphuric  acid  —  28  parts  of  nitrogen  as 
nitric  acid  =  34  parts  of  ammonia  (NHs).  Since  32  parts  of  sulphur 
as  sulphuric  acid  =  28  parts  of  nitrogen  as  nitric  acid,  one  gram  of 
sulphur  =  |  gram  of  nitrogen  in  the  titration  of  nitric  acid  with 
ammonia.  I  of  1020  calories  =  892  calories  as  the  correction 
which  is  applied  when  sulphuric  acid  is  titrated  as  nitric  acid; 
2200  —  892  =  1308  calories  per  gram  of  sulphur  as  an  additional 
correction  which  should  be  applied.  This  amounts  to  approxi- 
mately 13  calories  for  each  0.01  gram  of  sulphur  or  when  a  one- 
gram  sample  is  burned  in  the  calorimeter,  13  calories  for  each 
per  cent  of  sulphur  present  in  the  sample.  As  the  amount  of 
sulphur  is  frequently  as  high  as  4,  5  or  6  per  cent  this  correction 
is  often  large  and  there  is  no  valid  reason  for  omitting  it,  not- 
withstanding the  statement  often  seen  in  print  that  the  cor- 
rection for  the  sulphur  present  is  never  important. 

Ignition  of  the  iron  wire.  In  igniting  the  wire  fuse  a  current 
of  3  or  4  amperes  is  usually  required  and  an  electromotive  force 
of  15  to  20  volts  is  desirable.  Lower  voltage  such  as  a  current 
from  4  or  5  dry  cells  or  from  a  storage  battery  may  be  used  but  a 
low  voltage  requires  special  care  in  making  the  connection  or  fail- 


DETERMINING  THE  CALORIFIC   VALUE        101 

lire  to  ignite  often  results.  If  a  current  of  low  voltage  is  used, 
better  contact  between  the  platinum  terminals  and  the  wire  is 
secured  if  the  rods  and  wire  are  carefully  cleaned  with  emery 
paper.  Moistening  the  connection  between  the  terminals  and 
the  wire  with  a  drop  of  dilute  calcium 'chloride  solution  is  also  an 
advantage  in  securing  certainty  of  ignition.  The  usual  laboratory 
practice  of  using  a  high  voltage  current,  «,uch  as  the  current  from 
a  110-volt  lighting  circuit,  is  liable  to  result  in  errors  by  leakage 
of  the  current  after  ignition  of  the  wire  and  it  is  much  bafor  to 
introduce  a  resistance  coil  in  parallel  with  the  calorimeter  and 
shunt  off  only  a  portion  of  the  current  through  the  igniting  wire. 
In  this  way  the  voltage  through  the  calorimeter  can  easily  be  cut 
down  to  20  volts. 

To  lighting  circuit 


4-32C.P  lamps     p     Q    Q     Q 


German  silver 
resistance  coil 


witch 

circuit 


FIG.  6. — Diagram  of  Circuit  for  Igniting  Wire  Fuse. 

A  convenient  resistance  for  furnishing  the  proper  amount 
of  current  from  a  110-volt  lighting  circuit  is  to  mount  four  32- 
candle  power  lamps  in  parallel.  This  will  give  in  the  neighbor- 
hood of  3  J  to  4  amperes  of  current  which  is  ample  for  the  size  of 
wire  usually  used.  With  this  arrangement  a  5-  or  6-ohm  resis- 
tance coil  of  German  silver  or  other  high  resistance  wire,  as 
nichrome  or  climax  wire,  used  in  parallel  with  the  calorimeter 
is  a  simple  way  of  reducing  the  voltage.  (See  Fig.  6.)  Whatever 
be  the  connection  the  circuit  should  be  kept  closed  only  long 
enough  to  insure  burning  of  the  wire.  This  should  not  require 
at  most,  more  than  1  or  2  seconds.  If  more  time  is  required  more 
current  should  be  used.  With  leakage  of  current  through  the 
calorimeter  and  using  the  current  direct  from  a  110-volt  circuit, 
as  much  as  20  calories  per  second  may  be  transmitted  to  the 


102  COAL 

calorimeter,  which  is  an  error  too  large  to  be  neglected.  By  using 
the  shunt  and  keeping  the  voltage  below  20  the  he?it  from  4 
amperes  of  current  cannot  exceed  4  calories  per  second,  and  for 
the  time  that  the  circuit  is  usually  closed  it  is  a  small  error  com- 
pared to  the  possible  large  one  which  may  be  introduced  by  using 
the  110-volt  circuit  direct. 

Heat  developed  while  the  circuit  is  closed  for  ignition  of  the 
iron  wire.  The  iron  ignition  wire  used  (about  0.12  millimeter  in 
diameter  and  about  3  centimeters  between  the  terminals)  if  in 
good  contact  with  the  platinum  terminals  has  a  resistance  of 
less  than  one  ohm  and  the  amount  of  heat  developed  during  the 
fraction  of  a  second  that  the  current  passes  through  the  wire 
before  it  ignites  is  small.  The  resistance  of  the  calorimeter  it- 
self with  the  insulation  in  good  condition  is  several  millions  of 
ohms.  A  test  on  one  of  the  calorimeters  indicated  a  resistance  of 
upwards  of  twenty  million  ohms,  the  test  being  made  on  a  120- 
volt  circuit.  Pure  water  is  such  a  poor  conductor  that  after  im- 
mersion of  the  calorimeter  in  water  the  resistance  is  still  high 
(expressed  in  thousands  of  ohms). 

In  routine  work  the  distilled  water  used  to  surround  the  calo- 
rimeter bomb  is  used  over  and  over  again.  The  resistance  of  this 
water,  owing  to  traces  of  impurities,  is  not  so  great  as  that  of  the 
original  distilled  water,  but  its  resistance  is  still  high.  Tests  with 
water  which  had  previously  been  used  in  making  40  or  50  calo- 
rimeter determinations  showed  with  a  120-volt  circuit  about  1500 
ohms  resistance.  Tests  with  distilled  water  taken  directly  from 
the  laboratory  supply  showed  a  resistance  of  about  5000  ohms. 
With  the  resistance  in  excess  of  1000  ohms,  the  heating  effect 
due  to  leakage  of  current  is  quite  small  and  the  danger  from 
excessive  leakage  is  either  from  defective  insulation  of  the  bomb 
itself  or  from  the  use  of  water  containing  more  than  traces  of 
impurities.  The  possible  heating  effects  under  these  conditions 
are  discussed  in  the  next  paragraph. 

The  heat  developed  in  a  conductor  of  which  the  resistance 
is  R  ohms  by  current  of  I  amperes  in  a  time  of  t  seconds  is 
0.2387#/2  t  calories. 

Using  the  current  from  a  110-volt  circuit  with  4  thirty-two 
candle  power  lamps  in  parallel,  the  greatest  current  is  approxi- 
mately four  amperes.  With  the  resistance  coil  (5  ohms  re- 
sistance) in  the  circuit,  the  possible  heat  developed  by  passage  of 


DETERMINING  THE  CALORIFIC  VALUE        103 

current  through  the  calorimeter  is  small.  Before  the  ignition  of 
the  iron  wire  with  a  low  resistance  in  the  calorimeter  circuit 
(a  fraction  of  an  ohm)  practically  all  the  current  passes  through 
the  calorimeter,  but  since  I  cannot  exceed  4, 12  cannot  exceed  16, 
and  with  the  resistance  less  than  one  ohm,  the  product  of 
Q.2387RI2  is  less  than  4  calories  per  second. 

After  the  ignition  of  the  iron  wire  under  normal  conditions 
the  resistance  of  the  calorimeter  circuit  is  expressed  in  thousands 
of  ohms  and  practically  all  the  current  passes  through  the  coil 
having  only  5  ohms  resistance.  With  a  resistance  of  1500 
ohms  such  a  small  portion  of  the  current  flows  through  the 
calorimeter  that  its  heating  effect  is  less  than  one-tenth  calorie 
per  second.  With  defective  insulation  in  the  calorimeter,  or  with 
very  impure  water,  the  resistance  may  be  very  much  less  and  the 
possible  effects  under  these  conditions  should  be  considered. 

Take  as  special  cases,  resistances  of  10  ohms  and  100  ohms  in 
the  calorimeter.  With  the  circuit  closed  the  total  current  flowing 
through  the  resistance  coil  and  the  calorimeter  is  approximately 
4  amperes.  This  varies  slightly  on  account  of  small  changes  in 
the  total  resistance  of  the  circuit  due  to  the  variations  in  the 
calorimeter  resistance,  but  this  variation  in  current  is  so  small 
that  it  may  be  neglected  in  discussing  the  heat  effect  in  the 
calorimeter.  With  the  calorimeter  and  coil  connected  in  parallel, 
the  portion  of  the  total  current  passing  through  each  is  inversely 
as  its  resistance  is  to  the  sum  of  the  two  resistances.  With  10 
ohms  resistance  in  the  calorimeter  and  5  ohms  resistance  in  the 
coil  the  portion  of  current  passing  through  the  calorimeter  is 


With  100  ohms  resistance  in  the  calorimeter  the  portion  of  cur- 
rent passing  through  it  is: 

5          11 

„ * V/  A    C\    O      O  TY^  T\£^t*f^ 

100+5"  21 '21* 

Applying  the  formula  for  heat  production  with  10  ohms 
resistance  0.2387X10X(1.3)2  =  4  calories  per  second.  With  100 
ohms  resistance  0.2387  X 100 X(0.2)2  =  l  calorie  per  second. 


104  COAL 

With  resistances  between  1  and  10  ohms,  the  heating  effects 
are  very  close  to  4  calories.  With  resistances  of  over  10  ohms 
the  heating  effects  are  less  than  4  calories  per  second,  from  which 
it  appears  that  using  the  resistance  coil  in  circuit  under  no  con- 
dition can  the  leakage  of  current  per  second  be  large  enough  to 
very  appreciably  affect  the  results  obtained  on  the  calorific  value 
of  the  materials  tested. 

Resistance  coil  left  out  of  the  circuit.  Before  the  burning 
of  the  iron  wire  with  little  resistance  in  the  calorimeter  (less  than 
1  ohm)  approximately  4  amperes  of  current  will  pass  through  the 
calorimeter  and  the  heating  effect  is  small  (less  than  4  calories 
per  second).  After  the  burning  of  the  iron  wire,  under  normal 
conditions,  with  the  resistance  expressed  in  thousands  of  ohms, 
the  heating  effect  due  to  current  passing  through  the  calorimeter 
is  also  small.  In  the  special  test  upon  the  calorimeter  showing 
1500  ohms  resistance,  the  heating  effect  of  the  current  flowing 
through  the  circuit  is  between  two  and  three  calories  per 
second. 

^  With  the  lower  resistances,  which  may  occur,  due  to  defects 
in  the  insulation  or  the  use  of  very  impure  water,  the  effect  may  be 
of  considerable  magnitude  and  the  possible  effects  with  resistances 
between  1  and  1500  ohms  should  be  considered.  Small  increases 
in  the  resistance  in  the  calorimeter  diminish  the  amount  of  cur- 
rent flowing  only  slightly  and  the  amount  of  heat  produced  in- 
creases very  nearly  in  proportion  to  the  increase  in  resistance. 

With  1/2  and  3  ohms  resistance  in  the  calorimeter,  the  heat 
produced  is  approximately  4,  8  and  12  calories  per  second.  With 
larger  increases  in  resistance  the  change  in  current  due  to  the 
change  in  the  total  resistance  of  the  circuit  should  be  considered. 
The  total  resistance  of  the  circuit  is  the  resistance  of  the  lamps 
1(HO  ohms),  plus  the  resistance  in  the  calorimeter,  plus  the 
resistance  in  the  remainder  of  the  circuit.  The  resistance  of  the 
rest  of  the  circuit  is  small  and  the  total  resistance  outside  the 
calorimeter  is  therefore  approximately  that  of  the  lamps. 
(1(110  ohms)l.  The  total  resistance  of  the  circuit  is  approxi- 
mately 27  ohms  plus  the  resistance  of  the  calorimeter. 

E 

Ohm's  law  for  current  flowing  through  a  conductor  is  /=— . 

Considering  as  special  cases  the  effect  of  10,  100  and  1000  ohms 
resistance  in  the  calorimeter: 


DETERMINING  THE  CALORIFIC  VALUE        105 

(a)  With  10  ohms  resistance  the  current  is  — — — -  =  3  amperes. 

.27-j-lO 

(6)  With   100  ohms   resistance  the  current  is   — —    -=0.9 

27  -f- 100 

ampere. 

(c)  With  1000  ohms  resistance  the  current  is  -  —  =  0.1 

27+1000 

ampere. 

Applying  the  formula  for  heat  developed  in  the  calorimeter: 

(a)  0.2387  X 10 X(3)2  =  21  calories  per  second. 
(6)  0.2387XlOOX(0.9)2  =  19'calories  per  second. 
(c)  0.2387X1000X(0.1)2  =  3  calories  per  second. 

With  normal  conditions,  good  insulation  in  the  calorimeter 
and  water  practically  free  from  impurities,  the  effects  of  leakage 
of  current  are  unimportant,  but  with  defective  insulation  or  water 
high  in  impurities,  the  values  obtained  under  conditions  (a)  and 
(6)  show  that  the  possible  effects  during  the  time  that  the  switch 
is  closed  for  ignition  of  the  iron  wire  (about  2  or  3  seconds)  may 
be  of  such  magnitude  (40  to  60  calories)  as  to  change  appreciably 
the  calorific  value  obtained  for  the  materials  tested.  The  use  of 
the  resistance  coil  in  the  circuit  is  a  safeguard  against  such  pos- 
sible errors. 

Water  equivalent  of  the  calorimeter.  The  accuracy  of  the 
calorimetric  values  obtained  is  to  an  important  degree  depen- 
dent upon  the  accuracy  with  which  the  water  equivalent  of  the 
apparatus  has  been  determined.  This  may  be  determined  by 
several  methods: 

(1)  From  the  weights  of  the  different  parts  by  multiplying 
each   by  its   respective   specific  heat.       The  water  equivalent  is 
equal  to  the  sum  of  the  specific  heats  of  the  different  parts. 

(2)  By  adding  definite  weights  of  warmer  or  colder  water  to 
the  system  and  noting  the  corresponding  increase  or  decrease 
in  temperature. 

(3)  By  combustion  of  the  same  weight  of  material  but  vary- 
ing the  amount  of  water  used. 


106  COAL 

(4)  By  electric  methods. 

(5)  By  combustion  of  a  substance  of  known  calorific  value, 
as  naphthalene,  benzoic  acid  or  cane  sugar. 

The  author's  experience  with  the  first  three  of  these  methods 
has  not  been  very  satisfactory.  The  fourth  method  requires 
instruments  and  equipment  beyond  the  reach  of  most  commercial 
and  technical  laboratories  and  practically  the  only  available 
method  which  is  satisfactory  is  that  of  the  determination  by 
combustion  of  a  substance  of  known  calorific  value.  At  present 
the  materials  available  are  naphthalene,  benzoic  acid  and  cane 
sugar,  samples  of  which  together  with  certificates  of  their  heat- 
ing values  can  be  obtained  from  the  U.  S.  Bureau  of  Standards. 

The  calorific  values  of  these  materials  as  given  by  different 
authorities  are  as  follows; 

Naphthalene: 

Berthelot , 9692 

Atwater 9628 

Fischer  and  Wrede 9640 

U.  S.  Bureau  of  Standards  (standard  sample) .   9610 

Benzoic  acid: 

Berthelot 6322 

Stohmann 6322 

Fischer  and  Wrede 6333 

U.  S.  Bureau  of  Standards  (standard  sample) .  6320 

Cane  Sugar:   (sucrose) 

Stohmann 3955 

Berthelot 3961 

Fischer  and  Wrede 3957 

The  equation  for  determination  of  the  water  equivalent  (X) 
of  the  bomb,  bucket,  stirrer,  etc.,  is  as  follows: 

(Grams  of  water+X)  X  temperature  rise  =  the  amount  of 
sample  X  the  calorific  value + the  heat  due  to  the  ignition  of  the 
fuse+the  heat  due  to  the  formation  of  nitric  acid. 

Carefully  determined  water  equivalents  based  upon  a  num- 
ber of  determinations  upon  two  or  more  of  the  standard  materials 
ought  to  have  not  only  relatively  high  accuracy  but  enable  differ- 


DETERMINING  THE  CALORIFIC   VALUE         107 

ent  laboratories  to  work  upon  a  common  basis  and  make  their 
results  comparable. 

Errors  in  the  graduation  of  the  thermometer  used.  These 
errors  if  not  corrected  for  may  be  of  considerable  magnitude  and 
every  calorimeter  operator  should  take  some  means  of  insuring 
the  elimination  of  a  greater  part  of  the  errors  or  at  least  assuring 
himself  that  the  errors  are  not  large  enough  to  materially  affect 
the  accuracy  of  results.  Three  methods  of  checking  up  gradua- 
tion errors  are  available : 

(a)  Calibration  of  the  thermometer  by  divided  threads.  To  cali- 
brate accurately  by  this  method  requires  skill  and  attention  to 
details,  and  to  cover  the  working  range  several  threads  of  dif- 
ferent lengths  should  be  used  and  many  readings  taken.  With 
thermometers  in  which  the  mercury  threads  break  easily  and 
regularly,  the  method,  while  it  requires  considerable  time,  pre- 
sents no  serious  difficulties  aside  from  care  and  attention  to 
details  but  with  some  thermometers  the  author  has  found  it 
exceedingly  difficult  to  secure  threads  of  the  desired  length. 

As  an  example  of  the  method,  a  thermometer  graduated  from  15 
to  25°  and  graduated  to  hundredths  of  a  degree  was  checked  at 
each  whole  degree  by  the  use  of  threads  approximately  2°  and  5° 
in  length.  By  the  measurement  with  the  5°  thread  a  direct  deter- 
mination was  obtained  for  20°.  By  the  2°  thread  direct  deter- 
minations were  made  for  17  and  23°  and  as  secondary  determina- 
tions 19  and  21°;  16°  was  obtained  by  the  5°  thread  from  21°, 
24°  by  the  5°  thread  from  19°;  18°  and  22°  by  the  2°  thread 
from  20°.  A  number  of  readings  should  be  taken  for  each  of  the 
thread  lengths  at  a  slightly  different  position  and  the  mean  of 
these  readings  taken  as  the  length  for  that  position.  By  gently 
tapping  the  thermometer  the  thread  of  mercury  may  be  easily 
slipped  a  few  thousandths  of  a  degree  or  sufficiently  to  give  a 
new  set  of  readings.  For  example,  the  readings  on  the  5°  thread 
measurements  from  15  to  20°  =  5.028,  5.027,  5.028,  5.027, 
5.026,  5.027,  5.026,  5.027 -average  5.027°. 

20  to  25°  =  5.017,  5.019,  5.019,  5.018,  5.018,  5.017,  5.017, 
5.019,  5.018  =  average  5.018°.  The  sum  of  the  two  threads 
=  5.027+5.018  =  10.0450°.  According  to  the  Reichsanstalt 
certificate  for  this  thermometer  the  true  temperature  interval  of 
15  to  25°  is  10.02,  hence  the  true  length  of  the  measured  dis- 
tance, 10.045,  is  10.065  and  the  true  length  of  the  5°  thread  is 


108  COAL 

one-half  of  this  value  =  5.0325,  from  which  the  correction  at  20° 
is  5.0325  - 5.0270  =  +0.0055.  The  measurement  of  the  2°  thread 
and  the  establishment  of  other  points  by  the  measurements  with 
this  thread  is  done  in  the  same  manner. 

By  the  use  of  a  2|°  thread  in  connection  with  the  2°  and  5° 
threads  as  many  values  for  J°  readings  were  determined  as 
desired.  The  determination  of  the  correction  for  intermediate 
points  was  determined  graphically  by  plotting  the  curve  for  the 
determined  points. 

In  measuring  the  mercury  thread  the  operator  should  work 
in  a  room  at  a  uniform  temperature  or  make  corrections  for 
variations  in  the  observed  lengths  of  thread  at  different  tem- 
peratures. For  example,  a  thread  of  mercury  5°  long  for  a  two 
degrees  difference  in  temperature  varies  0.0016  degree  in  length 
so  that  temperature  differences  of  more  than  a  fraction  of  a  degree 
cannot  be  neglected  if  high  accuracy  is  desired.  The  readings 
should  be  made  by  means  of  a  telescope  mounted  on  a  fixed  sup- 
port movable  in  a  horizontal  direction.  A  cathetometer  laid  on 
its  side  is  very  satisfactory.  In  reading  the  thread  the  thermometer 
should  be  turned  so  that  the  ends  of  the  short  divisions  touch 
the  lower  edge  of  the  mercury  column  but  do  not  cross  it.  This 
position  of  the  ends  of  the  divisions  with  reference  to  the  ends  of 
the  mercury  thread  permits  sharper  readings. 

The  method  of  divided  threads  gives  only  the  relative  lengths 
of  the  degrees  and  in  itself  shows  nothing  as  to  their  absolute 
values  and  unless  the  highest  and  lowest  readings  have  been 
checked  the  numerical,  difference  is  assumed  as  the  true  value. 
This,  of  course,  may  make  all  the  degrees  too  large  or  too  small 
but  does  not  affect  their  relative  values  to  each  other,  and  in 
calorimeter  work  usually  what  is  desired  is  the  relative  value  and 
hence  a  failure  to  know  the  absolute  value  is  not  necessarily  of 
any  serious  consequence.  In  the  calibration  described  it  is 
assumed  that  the  errors  in  the  graduation  of  the  few  hundredths 
of  a  degree,  that  the  threads  are  longer  or  shorter  than  5,  2J  and 
2°,  cannot  materially  affect  the  results.  If  threads  are  used  of 
lengths  considerably  different  from  these  values,  this  assumption 
of  no  material  error  does  not  necessarily  hold  true.  For  fuller 
details  of  calibration  see  Physical  Measurements  by  Kohlraush 
or  text-books  on  Physics, 


DETERMINING   THE  CALORIFIC   VALUE        109 

(6)  Comparison  with  another  standard  thermometer.  Another 
method  of  determining  the  graduation  errors  is  to  compare  the 
thermometer  with  another  thermometer  which  has  already  been 
standardized.  Making  comparison  readings  to  thousandths  of  a 
degree  requires  special  equipment  and  special  precautions  to 
insure  thorough  mixing  of  the  liquid-  surrounding  the  bulbs  and 
to  prevent  rapid  temperature  changes  in  this  liquid. 

A  simple  and  inexpensive  equipment  which  the  author  has 
recently  made  use  of  in  this  work  is  a  500  c.c.  Dewar  vacuum 
flask.  The  two  thermometers  to  be  compared  are  inserted 
through  a  two-hole  cork  and  the  two  bulbs  brought  close  together 
but  not  quite  touching  one  another.  A  thin  strip  of  cork  inserted 
between  the  stems  just  above  the  bulbs  and  a  rubber  band 
wrapped  moderately  tight  around  both  stems  is  very  efficient 
for  holding  them  in  their  proper  positions.  The  upper  ends  of 
the  stems  should  be  secured  in  a  similar  manner.  In  making 
temperature  comparisons  the  flask  is  filled  about  three-fourths 
full  of  water  at  any  desired  temperature,  the  cork  and  thermom- 
eters inserted  into  position  and  the  water  around  the  bulbs  well 
mixed  by  inverting  the  flask.  The  readings  are  taken  through 
a  telescope,  the  stems  being  tapped  previous  to  taking  a  reading. 
A  number  of  pairs  of  readings  should  be  taken,  the  flask  being 
inverted  between  each  pair  of  readings.  The  average  of  the  read- 
ings of  each  thermometer  are  taken  as  the  reading  at  that  tem- 
perature. The  true  reading  for  each  thermometer  is  obtained 
by  adding  to  the  observed  reading  the  stem  correction  for  the 
thread  of  mercury  exposed  (see  page  110).  This  method  of 
comparison  has  the  advantage  that  owing  to  the  slow  radiation 
changes-  in  a  vacuum  flask  as  many  readings  as  desired  may  be 
taken  at  practically  the  same  temperature.  To  make  a  com- 
parison at  another  temperature  it  is  only  necessary  to  warm  or 
cool  the  contents  of  the  flask  to  approximately  the  temperature 
desired  and  take  a  series  of  readings  at  the  new  temperature. 
One  slight  objection  to  the  method  is  the  possibility  of  the  vacuum 
flask  going  to  pieces  and  destroying  the  thermometers.  This 
danger  is,  however,  very  slight  if  care  be  used  in  handling  the 
flask.  The  author  recommends,  however,  that  flasks  covered 
with  metal  or  canvas  be  used  so  that  in  case  of  possible  breakage 
there  will  be  no  danger  to  the  eyes  from  particles  of  flying  glass. 


110  COAL 

If  the  precautions  regarding  care  in  handling  the  flask  are  observed 
the  danger  of  breakage  is  very  small  and  the  author's  experience 
with  the  method  has  been  entirely  satisfactory. 

The  Bureau  of  Standards  at  Washington  is  equipped  to  do 
comparison  work  at  a  nominal  charge  and  in  many  cases  it  may 
be  preferable  for  the  calorimeter  operator  to  send  thermometers 
there  to  be  checked,  as  they  will  probably  do  it  better  than  he 
can  do  it  himself  and  the  Government  comparison  will  certainly 
carry  more  weight  in  a  court  of  law  than  a  comparison  by  a 
private  individual.  One  objection  to  having  the  Government 
calibrate  thermometers  is  that  several  weeks  necessarily  elapse 
before  they  are  returned  to  the  laboratory  and  in  a  busy  labo- 
ratory this  may  be  a  very  serious  objection. 

(c)  Comparison  of  the  readings  obtained  at  different  tempera- 
tures on  the  same  standard  material.  The  errors  in  graduation 
may  be  checked  by  running  a  number  of  check  determinations 
on  a  material  of  constant  composition  at  temperatures  covering 
the  working  range  of  the  thermometer.  For  example,  if  sets  of 
duplicate  determinations  on  naphthalene  made  at  a  number  of 
different  temperatures  covering  the  range  of  the  thermometer 
agree  closely,  evidently  the  graduation  errors  of  the  thermom- 
eter are  not  liable  to  be  serious.  Checking  a  thermometer  by 
this  method  may  not  be  regarded  as  an  actual  calibration  but  it 
does  serve  to  guard  against  any  serious  graduation  errors. 

Stem  temperature  corrections.  (Corrections  should  be  made 
to  the  observed  temperature  readings  on  account  of  differences 
between  the  temperature  of  the  emergent  stem  and  the  tempera- 
ture of  the  liquid  surrounding  the  bulb.)  Most  thermometers  are 
graduated  and  calibrated  for  total  immersion  of  the  stem  and 
bulb.  As  ordinarily  used  in  calorimetric  work  a  portion  of  the 
stem  containing  the  mercury  column  always  projects  above  the 
water  and  is  usually  either  colder  or  warmer  than  the  temperature 
of  the  water  surrounding  the  bulb.  Hence  to  secure  readings  for 
total  immersion  a  correction  must  be  applied.  As  ordinarily  ex- 
pressed this  correction  is  N(T— 0X0.00016,  where  N  =  degrees  of 
thread  above  the  liquid,  t  =  the  temperature  of  the  stem  as  observed 
by  an  auxiliary  thermometer,  T  =  the  temperature  of  the  bulb 
and  the  factor  0.00016  =  the  difference  between  the  expansion  of 
glass  and  mercury  for  one  degree  Centigrade.  With  N  =  5°,t=  15°, 


DETERMINING   THE  CALORIFIC   VALUE        111 

T  =  20°,  N(7X)X0.00016  =  0.004°,  the  amount  that  the  mercury 
reads  too  low.  Hence  this  correction  must  be  added.  With  T  =  \5, 
t  =  20,  the  value  is  this  amount  too  high  and  hence  has  to  be  sub- 
tracted from  the  observed  readings.  To  secure  the  true  tempera- 
ture difference  in  a  calorimetric  determination  corrections  of  both 
the  initial  and  final  readings  must  be  made.  This  correction  may 
be  done  at  one  operation  by  combining  the  two  corrections  into 
the  form  of  Kd(T ' +  T" '-S-t)  in  which  #  =  0.00016,  !F'  =  the 
initial  temperature  at  the  beginning  of  a  determination,  T"  =  the 
final  temperature  at  the  end  of  the  combustion  period,  d  =  ih& 
observed  temperature  rise  during  a  determination  or  T"  —  T", 
/S  =  the  scale  reading  to  which  the  thermometer  is  immersed, 
Z  =  the  temperature  of  the  emergent  stem  measured  by  an  aux- 
iliary thermometer.  Corrections  with  a  plus  sign  are  to  be  added 
to  the  observed  temperature  difference.  Corrections  with  a 
minus  sign  are  to  be  subtracted  from  the  observed  temperature 
difference.1 

Tabulation  of  stem  corrections.  A  convenient  method  for 
applying  the  corrections  is  to  solve  the  correction  equations  for 
the  differences  usually  found  in  calorimetric  work  and  arrange 
the  results  in  tabular  form  for  use  as  needed.  The  temperature 
rise  for  a  given  calorimeter  on  coal  work  ranges  from  2.4°  to  2.8° 
with  an  average  for  most  coals  of  between  2.5  and  2.7°.  The 
initial  temperature  should  be  2°  to  3°  below  the  room  tem- 
perature. For  example,  a  table  of  corrections  to  observed  tem- 
perature differences  computed  from  the  values  for  N(T  —  t) 
X  0.00016  for  the  temperature  at  the  beginning  and  end  of  the 
combustion  period  to  cover  the  above  mentioned  conditions  is 
as  follows:  The  values  given  are  for  observed  temperature  rises 
of  2.5°  and  2.7°  Centigrade,  where  N  =  length  of  the  emergent 
thread  at  the  beginning  of  the  combustion,  Tr  =  the  observed 
temperature  in  the  calorimeter  at  the  beginning  of  the  combus- 
tion, £  =  the  observed,  temperature  of  the  emergent  stem  meas- 
ured by  an  auxiliary  thermometer.  The  corrections  for  observed 
rises  of  temperature  of  2.5  and  2.7  degrees  and  for  different  values 
for  N  and  (T— t)  are  as  follows: 


Testing  of  Thermometer,  Bureau  of  Standard  Circular  No.  8. 


112 


COAL 


STEM  TEMPERATURE   CORRECTION  TABLE.1 


Initial 

Observed  Rise  in  Temperature  =2.5°. 

Length  of 

T-t  = 

Emergent 

Thread. 

N. 

-4° 

-3.5° 

-3° 

-2.5° 

-2° 

-1.5° 

1 

-0.5° 

-0° 

•  1° 

-  .  0002 

.0000 

+  .  0002 

+  .  0004 

+  .0006 

+  .  0008 

+  .0010 

+  .0012 

+  .0014 

1.5° 

.0000 

+  .  0002 

+  .  0004 

+  .  0006 

+  .0008 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

2° 

+  .0002 

+  .  0004 

+  .  0006 

+  .0008 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

2.5° 

+  .0004 

+  .  0006 

+  .0008 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

3° 

+  .  0006 

+  .  0008 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

+  .  0022 

3.5° 

+  .  0008 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

+  .  0022 

+  .0024 

4° 

+  .0010 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .0020 

+  .  0022 

+  .  0024 

+  .0026 

4.5° 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .0020 

+  .0022 

+  .0024 

+  .  0026 

+  .  0028 

5° 

+  .0014 

+  .0016 

+  .0018 

+  .0020 

+  .0022 

+  .  0024 

+  .  0026 

+  .0028 

+  .  0030 

5.5° 

+  .0016 

+  .0018 

+  .  0020 

+  .0022 

+  .  0024 

+  .0026 

+  .  0028 

+  .  0030 

+  .  0032 

6° 

+  .0018 

+  .  0020 

+  .  0022 

+  .  0024 

+  .  0026 

+  .0028 

+  .  0030 

+  .  0032 

+  .  0034 

6.5° 

+  .  0020 

+  .0022 

+  .  0024 

+  .0026 

+  .0028 

+  .  0030 

+  .  0032 

+  .  0034 

+  .  0036 

7° 

+  .  0022 

+  .  0024 

+  .  0026 

+  .  0028 

+  .0030 

+  .  0032 

+  .0034 

+  .0036 

+  .0038 

7.5° 

+  .  0024 

+  .0026 

+  .  0028 

+  .  0030 

+  .  0032 

+  .  0034 

+  .0036 

+  .0038 

+  .  0040 

8° 

+  .0026 

+  .  0028 

+  .  0030 

+  .  0032 

+  .0034 

+  .0036 

+  .0038 

+  .  0040 

+  .0042 

Observed  Rise  in  Temperature  =2.7°. 
T-t  = 


N. 

-4° 

-3.5° 

-3° 

-2.5° 

-2° 

-1.5° 

-1° 

-0.5° 

-0° 

1 

-.0001 

+  .0001 

+  .  0003 

+  .  000f> 

+  .  0007 

+  .  0009 

+  .0012 

+  .0014 

+  .0016 

1.5° 

+  .0001 

+  .  0003 

+  .  0005 

+  .  0007 

+  .  0009 

+  .0011 

+  .0014 

+  .0016 

+  .0018 

2° 

+  .  0003 

+  .  0005 

+  .  0007 

+  .  0009 

+  .0012 

+  .0014 

+  .0016 

+  .0018  +.0020 

2.5° 

+  .  0005 

+  .  0007 

+  .  0009 

+  .0011 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

+  .0022 

3° 

+  .  0007 

+  .  0009 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

+  .  0022 

+  .  0025 

3.5° 

+  .  0009 

+  .0011 

+  .0014 

+  .0016 

+  .0018 

+  .0020  +.0022 

+  .  0024 

+  .  0027 

4° 

+  .0012 

+  .0014 

+  .0016 

+  .0018 

+  .  0020 

+  .  0022 

+  .  0025 

+  .0027 

+  .  0029 

4.5° 

+  .0014 

+  .0016 

+  .0018 

+  .0020 

+  .0022 

+  .0025 

+  .0027 

+  .  0029 

+  .0031 

5° 

+  .0016  +.0018 

+  .  0020 

+  .0022 

+  .  0025 

+  .  0027 

+  .  0029 

+  .0031 

+  .  0033 

5.5° 

+  .0018 

+  .  0020 

+  .  0022 

+  .  0024 

+  .0027 

+  .  0029 

+  .0031 

+  .  0033 

+  .  0035 

6° 

+  .  0020 

+  .  0022 

+  .  0025 

+  .0027 

+  .  0029 

+  .0031  +.0033 

+  .  0035 

+  .  0038 

6.5° 

+  .  0022 

+  .  0024 

+  .  0027 

+  .  0029 

+  .0031 

+  .0033  +.0035 

+  .0037 

+  .0040 

7° 

+  .  0025 

+  .  0027 

+  .0029 

+  .0031 

+  .0033 

+  .0035  +.0038 

+  .  0040 

+  .  0042 

7.5° 

+  .0027 

+  .0029 

+  .0031 

+  .  0033 

+  .  0035 

+  .0037 

+  .  0040 

+  .0042 

+  .0044 

8° 

+  .  0029 

+  .0031 

+  .  0033 

+  .  0035 

+  .  0038 

+  .0040 

+  .  0042 

+  .  0044 

+  .  0046 

1  T  =the  initial  observed  temperature  in  calorimeter. 

t  =the  observed  temperature  of  emergent  stem  measured  by  auxiliary  thermometer. 

From  these  values  the  corrections  for  &uy  conditions  usually 
found  can  be  approximated  readily  to  about  0.001°.  To  secure 
this  degree  of  accuracy  N  and  T  —  t  need  be  read  to  only  the 
nearest  0.5°  and  the  observed  temperature  rise  need  not  be 
closer  than  0.1°  to  the  amount  of  rise  on  which  the  values  are 
calculated.  For  example,  corrections  for  rises  between  2.4  and 
2.6  can  be  taken  from  the  correction  based  on  2.5°  and  correc- 
tions for  rises  between  2.6  and  2.8  taken  from  the  values  based  on 


DETERMINING   THE  CALORIFIC   VALUE        113 

a  rise  of  2.7°  without  any  appreciable  error.  As  an  illustration, 
suppose  the  initial  temperature  of  the  calorimeter  7  =  16. 5°,  the 
temperature  of  the  emergent  stem  £  =  19°,  the  scale  reading  of 
the  emergent  stem  =  12°  and  the  observed  temperature  differ- 
ence during  the  determination  =  2. 8°.  Then  A^  =  16. 5  — 12  =  4.5. 
T  —  £  =  16. 5  — 19=  —2.5.  From  the  table  the  correction  corre- 
sponding to  initial  thread  length  N  of  4.5  and  T—t=  —2.5  and  an 
observed  rise  of  2.7  degrees  is  found  to  be  +0.002°.  Inspection 
of  the  table  furthermore  shows  that  in  a  difference  in  rise  of 
2.5  to  2.7  the  correction  change  is  only  about  0.0002°,  hence  the 
additional  correction  corresponding  to  the  rise  of  2.8°  instead 
of  2.7°  is  approximately  0.0001°  and  can  be  entirely  neglected, 
which  makes  the  observed  correction  approximately +0.002. 

As  may  be  observed  from  the  table,  the  amount  of  the  cor- 
rection varies  from  practically  nothing  up  to  0.005°.  With  a 
water  equivalent  for  the  calorimeter  of  3000  calories  this  latter 
amount  is  equivalent  to  a  correction  of  15  calories,  a  possible 
correction  too  large  to  be  omitted  if  a  high  standard  of  accuracy 
is  desired. 

For  similar  working  conditions  where  the  correction  was 
omitted  in  standardizing  the  calorimeter  with  naphthalene,  ben- 
zoic  acid  or  cane  sugar,  its  omission  on  determinations  made  on 
coal  introduces  little  or  no  error  as  one  correction  practically 
balances  the  other.  Unfortunately  similar  working  conditions 
day  after  day  cannot  be  maintained  and  the  stem  corrections 
at  different  times  may  vary  from  less  than  0.001°  to  over  0.004°. 
The  carrying  out  of  the  values  of  other  corrections,  such  as  titre 
and  burning  of  wire  fuse,  to  fractions  of  a  calorie  and  then  omit- 
ting this  correction  entirely  is  to  say  the  least  not  very  consistent 
practice,  and  the  author  believes  that  the  use  of  a  table  similar 
to  the  one  given,  whereby  the  errors  can  be  eliminated  regularly 
instead  of  hit  or  miss  is  well  worth  the  little  extra  trouble  which 
its  use  involves. 

Correction  for  variations  in  the  specific  heat  of  water.  Since 
the  specific  heat  of  water  is  different  for  different  temperatures 
exact  calorimeter  determinations  require  corrections  for  deter- 
minations made  at  temperatures  other  than  that  at  which  the 
water  equivalent  of  the  calorimeter  was  determined.  In  making 
this  correction  the  use  of  a  thermal  capacity  table  for  water  is  a 


114 


COAL 


great  convenience.     Such  a  table  based  on  Barnes'  values  for 
specific  heats  of  water  is  given  by  Loeb  1  as  follows : 

SPECIFIC  HEAT  AND  THERMAL  CAPACITY  OF  WATER  FROM  0°  TO  50°  C. 


Temp. 
°C. 

Specific 
Heat. 

Thermal 
Capacity. 

Difference. 

Temp. 

°c. 

Specific 
Heat. 

Thermal 
Capacity. 

Difference. 

0 

1.00940 

0.00000 

25 

.99806 

25.05131 

i 

1.00855 

1.00898 

1.00898 

26 

.99795 

26.04932 

.99801 

2 

1.00770 

2.01710 

1.00812 

27 

.99784 

27.04720 

.  99788 

3 

1.00690 

3.02440 

1.00730 

28 

.99774 

28  .  04499 

.  99779 

4 

1.00610 

4.03090 

1.00650 

29 

.99766 

29.04269 

.99770 

5 

1.00530 

5.03660 

1.00570 

30 

.99759 

30.04031 

.  99762 

6 

1.00450 

6.04150 

1.00490 

31 

.99752 

31  .  03786 

.99755 

7 

1.00390 

7.04570 

1.00420 

32 

.99747 

32.03536 

.99750 

8 

1.00330 

8.04930 

1.00360 

33 

.99742 

33.03280 

.99744 

9 

1.00276 

9.05233 

1.00303 

34 

.997,38 

34.03020 

.99740 

10 

1.00230 

10.05486 

1.00253 

35 

.  99735 

35  .  02757 

.99737 

11 

1.00185 

11.05694 

1.00208 

36 

.99733 

36  .  02491 

.  99734 

12 

1.00143 

12.05858 

1  .  00164 

37 

.99732 

37.02224 

.99733 

13 

1.00100 

13.05980 

1.00122 

38 

.  99732 

38.01956 

.99732 

14 

1.00064 

14.06062 

1.00082 

39 

.99733 

39.01689 

.99733 

15 

1.00030 

15.06109 

1.00047 

40 

.99735 

40.01422 

.99733 

16 

1.00000 

16.06124 

1.00015 

41 

.99738 

41.01159 

.99737 

17 

.99970 

17.06109 

.99985 

42 

.99743 

42.00899 

.99740 

18 

.  99941 

18.06064 

.99955 

43 

.99748 

43  .  00644 

.99745 

19 

.99918 

19.05994 

.99930 

44 

.99753 

44  .  00395 

.99751 

20 

.99895 

20.05900 

.99906 

45 

.99760 

45.00152 

.99757 

21 

.  99872 

21.05783 

.99883 

46 

.  99767 

45.99916 

.99764 

22 

.99853 

22.05645 

.99862 

47 

.99774 

46.99686 

.99770 

23 

.99836 

23.05490 

.99845 

48 

.99781 

47.99464 

.99778 

24 

.  99820 

24.05318 

.  99828 

49 

.99790 

48.99250 

.99786 

25 

.  99806 

25.05131 

.99813 

50 

.99800 

49.99045 

.99795 

From  this  table  the  differences  in  the  thermal  capacity  of  water 
throughout  the  temperature  range  at  which  calorimeter  'work  is 
usually  done  may  easily  be  calculated.  For  example,  with  a 
Mahler  calorimeter  having  a  water  equivalent  of  approximately 
500  calories  and  using  2400  grams  of  water  in  the  calorimeter, 
the  water  equivalent  of  the  system  equals  approximately  2900 
calories  and  a  rise  of  3°  corresponds  approximately  to  8700  calories 
of  heat.  As  this  is  several  hundred  calories  higher  than  the 
heating  value  of  the  best  coal,  3°  may  be  taken  as  representing 
the  maximum  rise  of  the  thermometer  during  a  determination 
where  one  gram  of  coal  is  used.  The  thermal  capacity  of  2400 


1  Jr.  Ind.  and  Eng.  Chcm.,  1911,  p.  175. 


DETERMINING   THE  CALORIFIC   VALUE        115 


grams  of  water  for  the  different  3°  intervals  from  14  to  30°  C. 
is  as  follows: 


Temperature. 

Thermal 
Capacity. 

Difference. 

Temperature. 

Thermal 
Capacity. 

Difference. 

14  to  17° 

7201.13 

2  21 

21  to  24° 

7188.84 

1.32 

15  to  18° 

7198.92 

2  04 

22  to  25° 

7187.66 

1.18 

16  to  19° 

7196.88 

1  90 

23  to  26° 

7186  .  61 

1.05 

17  to  20° 

7194.98 

1  72 

24  to  27° 

7185.  65 

0.96 

18  to  21° 

7193  .  26 

1  64 

25  to  28° 

7184.83 

0.82 

19  to  22° 

7191.62 

1  46 

26  to  29° 

7184.09 

0.74 

20  to  23° 

7190.16 

27  to  30° 

7183.46 

0.63 

From  which  the  corrections  corresponding  to  a  water  equiva- 
lent determination  made  at  any  particular  temperature  may 
readily  be  tabulated.  For  example,  assume  that  the  water  equiv- 
alent of  the  calorimeter  is  determined  at  the  temperature  range 
18  to  21°.  Then  for  determinations  made  upon  coal  for  this 
range  no  correction  is  necessary  but  for  determinations  made  at 
temperatures  above  or  below  corrections  should  be  used.  Calcu- 
lating from  the  differences  in  the  thermal  capacity  at  different 
temperatures,  the  correction  for  each  thousand  calories  of  heat 
developed  by  the  coal  is  as  follows: 


Temperature. 

Correction  Calories. 

Temperature. 

Correction  Calories. 

14  to  17° 

+0.90 

21  to  24° 

-0.51 

15  to  18° 

+0.65 

22  to  25° 

-0.64 

16  to  19° 

+0.42 

23  to  26° 

-0.76 

17  to  20° 

+0.20 

24  to  27° 

-0.87 

18  to  21° 

no  correction 

25  to  28° 

-0.97 

19  to  22° 

-0.19 

26  to  29° 

-1.05 

20  to  23° 

-0.35 

27  to  30° 

-1.13 

From  which  it  may  be  seen  that  in  a  coal  having  a  calorific 
value  of  7000  calories  the  corrections  to  be  applied  range  from 
the  extremes  of  +6  calories  to  —8  calories.  If  the  water  equiva- 
lent determination  of  the  calorimeter  instead  of  being  made  at  an 
intermediate  temperature  as  18  to  21°  is  made  at  a  higher  or 
lower  range,  as  25  to  28°  or  15  to  18°,  the  maximum  correction 
for  a  determination  would  be  greater  than  the  8  calories  in  the 
case  assumed. 


116  COAL 

With  a  water  equivalent  made  at  intermediate  temperatures 
the  correction  to  be  applied  is  usually  not  large  and  can  be 
neglected  in  routine  work,  but  for  work  of  the  highest  accuracy, 
this  correction  must  be  used  along  with  other  corrections  of 
similar  magnitude,  which  have  been  already  discussed. 

Effect  of  hydrogen  in  the  sample  upon  observed  calorific 
value.  Any  hydrogen  in  the  sample  not  already  combined  with 
oxygen  during  combustion  unites  with  oxygen  to  form  water 
which  condenses  and  the  remaining  gas  expands  as  a  result  of  the 
disappearance  of  this  oxygen.  This  expansion  absorbs  heat,  the 
amount  absorbed  being  proportional  to  the  amount  of  oxygen 
which  disappears.  Approximately  1.36  calories  are  absorbed  for 
each  0.01  gram  of  hydrogen  which  unites  with  oxygen.  For  coals 
containing  4  per  cent  of  available  hydrogen  the  correction  amounts 
to  about  5|  calories. 

The  calculation  of  this  effect  in  brief  is  as  follows:  The 
mechanical  equivalent  of  heat  has  been  determined  as  42,350 
gram-centimeters  =  1  calorie.  In  consideration  of  gas  volumes 

pV 

—  is  known  to  be  a  constant  where  V  is  the  volume  in  gram- 
molecules.  Let  p  =  1  atmosphere  pressure  =  1033  grams  per  square 
centimeter.  Let  V  =  l  gram  molecular  volume  of  gas  =22.4 
liters  =  22400  cubic  centimeters.  Let  77  =  273°  absolute  =  0°  C. 

pV     1033X22,400 
Substituting  these  values  for  — = =84,750  gram- 

J.  2i  t  o 

centimeters,     which    expressed    in    calories  =  84, 750  -^  42,350  =  2 

pV 
calories.      —  =  2  calories  or  pV  =  2T  which  =  546  calories.     Two 

grams  of  hydrogen  at  0°  C.  and  760  mm.  pressure  =  22.4  liters. 
0.01  gram  of  hydrogen  =  0.1 12  liter.  The  equivalent  volume  of 
oxygen  uniting  with  0.01  gram  of  hydrogen  =  0.056  liter.  With 
pF  =  546  calories,  22.4  liters  =  546  calories,  from  which  0.056 
liter  =  1.36  calories  as  the  amount  of  heat  absorbed  as  a  result  of 
the  contraction  of  the  oxygen  equivalent  to  0.01  gram  of  hydro- 
gen. Naphthalene  (CioHg)  contains  about  6J  per  cent  hydrogen, 
hence  if  the  heat  as  burned  under  conditions  of  constant  pres- 
sure is  desired,  the  observed  calorific  value  obtained  in  the 
bomb  calorimeter  should  be  increased  by  6jX  1.36  =  about  8.5 
calories. 

The  value  given  for  naphthalene  by  the  Bureau  of  Standards 


DETERMINING  THE  CALORIFIC  VALVE        117 

is  the  observed  value  obtained  in  a  bomb  calorimeter  and  in 
using  naphthalene  as  a  standard  for  determining  the  water  equiv- 
alent of  another  calorimeter  the  observed  value  is  the  one  that 
should  be  used.  If,  however,  the  heating  value  of  naphthalene 
is  compared  with  the  heating  value  of  carbon  or  coal  as  burned 
under  ordinary  conditions  the  observed  value  should  be  increased 
by  8.5  calories. 

The  available  hydrogen  in  coal  runs  from  2J  to  4J  per  cent 
which  corresponds  to  corrections  of  from  4J  to  7  calories.  Petro- 
leum contains  about  14  per  cent  hydrogen  which  corresponds  to 
a  correction  of  about  20  calories. 

The  formation  of  nitric  and  sulphuric  acids  during  combustion 
likewise  causes  a  small  absorption  of  heat  on  account  of  the  oxy- 
gen used  up.  The  amount  absorbed  =  0.58  calorie  for  0.01  gram 
of  nitrogen  and  0.25  calorie  for  0.01  gram  of  sulphur,  and  for  the 
amounts  of  nitrogen  and  sulphur  in  coal  this  can  be  neglected 
without  any  appreciable  error. 

For  the  highest  grade  of  work  the  correction  due  to  hydro- 
gen should  be  taken  into  consideration  and  applied.  However, 
its  omission  in  commercial  work  cannot  cause  any  very  large  error. 

Use  of  a  cover  on  the  water  jacket  of  the  calorimeter.  A 
cover  on  the  water  jacket  is  presumably  an  improvement  over 
the  common  open  top  calorimeter  owing  to  the  smaller  radiation 
changes  but  unless  used  properly  a  cover  may  introduce  errors 
larger  than  the  errors  that  are  supposed  to  be  eliminated,  and  in 
using  a  covered  calorimeter  the  author  strongly  advises  begin- 
ning the  determination  at  a  temperature  several  degrees  below 
the  jacket  water  temperature 'so  that  the  temperature  of  the  calo- 
rimeter at  the  end  of  the  combustion  period  will  still  be  below  the 
temperature  of  the  surrounding  jacket  water.  If  this  precaution 
is  not  observed  a  high  final  rate  is  very  apt  to  be  obtained  due  to 
the  surrounding  jacket  being  below  the  dew  point,  as  compared 
to  the  surface  of  the  water  in  the  calorimeter  bucket,  and  a  much 
more  rapid  evaporation  from  the  surface  of  the  calorimeter 
water  occurs  during  the  final  period  than  at  the  beginning  period 
when  the  jacket  walls  are  warmer  than  the  water  in  the  calo- 
rimeter. 

Impurities  in  oxygen.  Compressed  oxygen  of  a  high  degree 
of  purity  for  calorimetric  work  is  readily  obtained  on  the  market 
at  a  comparatively  low  cost.  The  author  has  never  found  hydro- 


118  COAL 

carbons  present  in  the  oxygen  in  sufficient  amounts  to  seriously 
affect  the  calorimeter  determination.  Their  presence,  however, 
is  always  a  possibility  and  a  safe  rule  which  should  be  strictly 
followed  is  to  run  blanks  on  naphthalene,  benzoic  acid,  or  cane 
sugar  on  every  new  tank  of  oxygen  and  if  impurities  of  any  con- 
sequence are  found  they  should  be  corrected  for  or  better  still 
the  tank  should  be  rejected  and  a  fresh  supply  of  oxygen  obtained. 


CHAPTER  VI 
SUMMARY  OF  CHEMICAL  DETERMINATIONS  AND  RECORDS 

A  SUMMARY  of  these  may  help  to  make  clear  just  what  relation 
the  various  determinations  have  to  one  another,  and  to  the  sam- 
ple of  coal  and  serve  to  prevent  uncertainty  and  confusion  in  the 
meaning  and  use  of  the  terms. 

Chemical  records.  The  air  drying  of  the  coarse  sample  and 
the  analytical  determinations  on  the  air-dried  sample  neces- 
sitate the  recalculating  of  results  to  obtain  the  analyses  of  the 
"  sample  as  received."  Some  of  the  analytical  records  of  a  well 
conducted  laboratory  are  shown  by  the  following  record  of  a 
regular  laboratory  sample: 

Laboratory  sample  number 1561 

Per  Cent. 


Loss  of  moisture  in  air-drying  of  coarse  sample       3. 10 
Analysis  of  air-dried  sample: 

Proximate: 

Moisture 1.01 

Volatile  matter 29 . 53 

Fixed  carbon 62 . 67 

Ash..  6.79 


100.00 
Ultimate: 

Hydrogen 5 . 04 

Carbon 79.35  . 

Nitrogen 1 . 63 

Oxygen 6 . 39 

Sulphur 0.80 

Ash..  6.79 


100.00 

Calorific  value  determined,  7984  calories  =  14,371  B.t.u. 

Calorific  value  calculated  from  ultimate  analysis,  7890  calories  =  14,202  B.t.u. 

119 


120  COAL 

The  analysis  of  the  "  sample  as  received  "  is  obtained  from 
the  results  on  the  air-dried  sample  by  multiplying  each  result  by 


_ 

-  and  adding  to  the  moisture  result  so  obtained  the  3.10 
J-UU 

per  cent  loss  on  the  coarse  sample  and  to  the  hydrogen  and  oxy- 
gen results  so  obtained  this  3.10  per  cent  moisture  loss  in  the 
proportion  in  which  the  two  elements  unite  to  form  water  or  -J- 
of  the  moisture  loss  to  the  hydrogen  and  |  of  the  loss  to  the 
oxygen. 

Performing  these  operations,  the  analysis  on  the  "  sample  as 
received  "  is  as  follows: 

"  Sample  as  received: 

Per  Cent. 


Proximate: 

Moisture 4 . 08 

Volatile  matter. . » 28.61 

Fixed  carbon 60 . 73 

Ash..  6.58 


100.00 

Ultimate: 

Hydrogen 5 . 23 

Carbon 76 . 89 

Nitrogen 1 . 58 

Oxygen 8.95 

Sulphur 0.77 

Ash..  6.58 


100.00 

Calorific  value  determined,  7736  calories  =  13, 925  B.t.u. 

Calorific  value  calculated  from  ultimate  analysis,  7645  calories  =  13, 761  B.t.u. 

Dry  coal.  The  result  on  the  air-dried  sample  must  not  be 
confounded  with  the  "  dry  coal  "  of  the  mechanical  engineer, 
which  may  be  obtained  from  either  of  the  above  ultimate  anal- 
yses by  subtracting  from  the  hydrogen  and  oxygen  shown  in  the 
analysis  the  amount  of  hydrogen  and  oxygen  present  in  the  mois- 
ture of  the  proximate  analysis  corresponding  to  the  ultimate,  then 
dividing  each  of  these  remainders  and  each  of  the  other  per- 
centages of  the  ultimate  analysis  by  100  minus  the  moisture 
present  in  the  proximate  analysis. 


SUMMARY   OF   CHEMICAL  DETERMINATIONS     121 

Performing  these  operations,   the  ultimate   analysis  for  the 
dry  coal  "  on  this  sample  is  as  follows: 

Hydrogen 4 . 98 

Carbon 80.15 

Nitrogen 1 . 65 

Oxygen 5 . 55 

Sulphur 0.81 

Ash..  6.86 


100.00 

The  volatile  matter,  fixed  carbon  and  ash  of  the  proximate 
analysis  reduced  to  the  "  dry  coal  "  are: 

Volatile  matter 29 . 83 

Fixed  carbon 63 . 31 

Ash . .  6 . 86 


100.00 

Calorific  value  determined  =  8065  calories,  14,517  B.t.u. 

Calorific  value  calculated  from  ultimate  analysis,  7970  calories  =  14,346  B.t.u. 

This  seems  to  be  a  multiplication  of  results  but  all  appear 
to  be  necessary.  The  "  as  received  "  results  certainly  cannot  be 
dispensed  with,  as  they  represent  the  actual  sample.  The  results 
on  the  air-dried  sample  are  the  actual  results  obtained  in  the 
laboratory  and  are  of  interest  as  showing  the  analysis  of  the  coal 
when  in  an  approximately  air-dried  condition.  The  chemist  has  no 
use  for  the  "  dry  coal  "  results  but  it  is  necessary  for  the  mechan- 
ical engineer  in  calculating  the  heat  balance  by  the  code  pre- 
scribed by  the  American  Society  of  Mechanical  Engineers,  who 
report  results  calculated  to  a  "  dry  coal  "  basis.  The  "  dry  coal  " 
basis  is  also  convenient  in  comparing  boilers  burning  the  same  or 
similar  coals. 


CHAPTER  VII 
IMPROVEMENT  OF  COAL  BY  WASHING 

THE  proximate  analysis  of  coal  may  show  the  need  of  im- 
provement by  washing,  but  as  these  results  show  only  the 
amounts  of  sulphur  and  ash  present  they  furnish  no  information 
of  whether  or  not  the  impurities  or  sulphur  may  be  removed  by 
treatment.  Whether  or  not  coal  can  be  improved  by  washing 
depends  upon  the  mode  and  nature  of  the  occurrence  of  the  ash 
and  sulphur  present. 

Sulphur.  If  present  as  organic  sulphur  it  cannot  be  removed 
by  washing.  If  present  as  pyrite,  finely  disseminated  through  the 
coal,  it  cannot  be  removed  by  washing  to  any  considerable  extent. 
If  present  as  pyrite  in  flakes  or  lumps  of  appreciable  size  it  may 
be  removed  by  washing,  especially  if  the  coal  is  crushed  suffi- 
ciently to  separate  a  large  part  of  the  pyrite  from  the  surround- 
ing coal. 

Ash.  The  same  remarks  as  to  distribution  of  sulphur  are 
applicable  to  ash.  If  the  ash  is  disseminated  uniformly 
through  the  coal,  washing  will  effect  little  improvement.  If  on 
the  other  hand  a  large  part  of  the  total  ash  is  present  as  slate 
or  as  bone  coal,  washing  will  result  in  a  decided  lowering  of  the 
ash  content  in  the  washed  coal.  Clean  coal  has  a  specific  gravity 
of  about  1.27  to  1.32.  The  specific  gravity  of  bone  coal,  slate  and 
pyrite  ranges  from  about  1.4  to  5.  Laboratory  tests  on  small 
portions  of  the  coal  are  often  sufficient  to  show  the  possible 
improvement  of  the  coal  by  washing.  For  illustration,  if  on  float- 
ing the  coal  on  a  calcium  chloride  solution  of  1.35  specific  gravity 
a  large  portion  sinks,  evidently  the  amount  of  clean  coal  is  low 
and  the  amount  of  bone  coal  is  high.  If  on  the  other  hand  only 
a  small  amount  of  comparatively  very  heavy  material  sinks, 
the  indications  are  that  a  considerable  part  of  the  ash  and  sul- 
phur is  present  in  a  comparatively  small  amount  of  heavy  res- 
idue. By  taking  weighed  amounts  of  coal  at  different  sizes  and 
subjecting  these  weighed  amounts  to  treatment  on  solutions  of 

122 


IMPROVEMENT  OF  COAL  BY   WASHING        123 

different  specific  gravities  ranging  from  1.35  to  1.55  or  1.65,  a 
separation  into  low,  medium  and  high  ash  material  may  be 
effected.  From  the  amounts  and  analyses  of  these  different 
materials  the  distribution  of  the  ash  and  sulphur  can  be  deter- 
mined and  the  possible  improvement  of  the  coal  by  washing 
estimated. 

The  apparatus  used  for  making  washing  tests  may  be  very 
simple  but  if  much  testing  is  to  be  done,  equipment  adapted  to 
the  work  should  be  obtained.  Some  of  the  necessary  equip- 
ment is  as  follows: 

(1)  A  set  of  sieves,  J-,  f-  and  J-inch,  20-mesh  and  60-mesh. 

(2)  For  the  washing  work  ordinary  laboratory  beakers,  fun- 
nels, etc.,  may  be  used  but  a  better  equipment  is  as  follows: 

For  holding  the  washing  solution,  two  or  more  copper  cyl- 
inders about  5  inches  in  diameter  by  8  inches  deep  fitted  with  a 
handle  for  lifting  and  with  a  lip  for  pouring.  For  filtering,  two 
or  more  7-inch  copper  funnels  having  a  stem  about  3  inches  long 
by  1^  inch  in  diameter  and  fitted  with  a  60-mesh  brass  filter 
gauze  2  to  3  inches  in  diameter.  For  skimming  off  the  light  coal 
a  semi-circular  gauze  skimmer  fitted  with  a  handle  and  having 
the  circumference  of  the  skimmer  just  a  trifle  smaller  than  the 
circumference  of  the  copper  cylinder. 

The  process  is  as  follows :  The  sample  for  testing  is  put 
through  a  jaw  crusher  and  reduced  till  it  all  passes  a  J-inch  sieve. 
In  crushing  care  is  taken  not  to  force  the  feeding  of  the  sample 
through  the  crusher  as  choking  of  the  crusher  tends  to  make  an 
undue  amount  of  fine  sample.  After  the  sample  is  so  reduced 
that  it  all  passes  the  coarse  sieve  the  very  fine  portion — 60-mesh 
and  finer — is  sifted  out  as  this  fine  portion  slimes  badly  and  cannot 
be  successfully  washed.  The  amount  of  this  fine  portion  is 
usually  between  f  and  4  per  cent  of  the  total  sample.  It  is  weighed 
and  analyzed  for  ash  and  sulphur  if  desired.  In  sifting  out  this 
fine  portion  a  preliminary  sifting  on  a  20-mesh  sieve  is  desirable, 
sifting  that  portion  which  passes  through  the  20-mesh  on  to  the 
60-mesh  and  adding  the  over-size  of  the  60-mesh  to  the  over-size 
of  the  20-mesh.  This  is  much  more  rapid  and  satisfactory  than 
the  attempt  to  sift  the  entire  sample  direct  on  the  60-mesh. 

The  copper  cylinder  is  filled  about  two-thirds  full  of  washing 
solution,  and  about  one-half  of  the  coal  to  be  washed  (assuming 
3  to  4  pounds  as  the  amount  to  be  tested)  is  poured  into  the  cyl- 


124 


COAL 


inder  and  stirred  up  well  to  insure  thorough  wetting  and  freeing 
from  air  bubbles.  The  lighter  portion  is  then  skimmed  off  and 
transferred  to  the  7-inch  funnel.  The  remainder  of  the  sample  is 
then  poured  into  the  cylinder  and  stirred  up  as  before  and  the 
lighter  portion  skimmed  off  and  added  to  the  first  portion  in  the 
funnel.  The  heavy  portion  is  then  filtered  through  another  fun- 
nel. As  soon  as  the  light  and  heavy  portions  have  drained,  the 
washing  solution  filtrate  is  removed  (to  be  used  for  other  tests) 
and  the  samples  washed  with  water.  They  are  then  air-dried, 
weighed,  crushed  and  analyzed  for  moisture,  ash  and  sulphur. 

If  J-inch  size  samples  are  to  be  tested  somewhat  larger  sam- 
ples— 6  to  8  pounds — should  be  used  for  the  tests,  in  which  case 
the  copper  cylinders  and  funnels  should  be  proportionately 
larger.  The  washing  solutions  used  are  calcium  chloride  and 
zinc  chloride.  In  separation  of  very  clean  coal  a  solution  as  low 
as  1.33  in  specific  gravity  may  be  used.  The  usual  solution  used 
has  a  specific  gravity  of  1.35.  In  separation  of  coal  with  moder- 
ate amounts  of  ash,  solutions  of  specific  gravity  from  1.4  to  1.45 
are  used  and  in  separating  bone  coal,  etc.,  solutions  with  a  specific 
gravity  as  high  as  1.6  to  1.7  may  be  used. 

The  method  of  calculating  and  the  results  obtained  may  be 
shown  by  the  following  tests  taken  from  Bulletin  No.  9  of  the 
Ohio  Geological  Survey,  pages  306-307. 

PUBLICATION  No.  11 
Unwashed  coal,  ash  10.81,  sulphur  5.04 


Portion. 

Ash. 

Sulphur. 

Compared  with 
Original  Sample. 

Ash. 

Sulphur. 

\  inch  to  iro  inch  = 

94.52 

66.7 

27.82 

6.48 
21.05 

3.68 
8:83 

4.32 

5.86 

0.50 

2.45 

2.46 
0.23 

Lighter  than  1.35      .      = 

Heavier  than  1.35.  ...*.= 
^5  inch  and  finer  ...      = 

4  62 

5  inch  to  iTo  inch               = 

96.9 

87.3 
9.6 

7.83 
33.88 

4.20 
14.24 

10.68 

6.84 
3.25 

0.24 

5.14 

3.67 
1.37 

0.11 
5.15 

Lighter  than  1.45  = 
Heavier  than  1.45  = 

^V  inch  and  finer  .  .      .  .  = 

2.2 

10.33 

IMPROVEMENT  OF  COAL  BY   WASHING        125 


PUBLICATION  No.  29 
Unwashed  coal,  ash  8.94,  sulphur  2.11 


Portion. 

Ash. 

Sulphur. 

Compared  with 
Original  Sample. 

Ash. 

Sulphur. 

\  inch  to  «Y>  inch  = 
Lighter  than  1.35  = 
Heavier  than  1.35  = 

-g-o  inch  and  finer            .  = 

99.3 
0.5 

85.5 
13.8 

6.16 
27.64 

1.14 

8.83 

5.27 
3.81 

0.04 
9.12 

0.97 
1.22 

0.01 
2.20 

COKE 


Percentage 
Yield. 

Ash. 

Sulphur. 

Phos. 

Coke  from  unwashed  coal  = 
Percentage  of  the  sulphur  in  the  coal 
left  in  the  coke  = 
Coke  from  washed  coal  lighter  than 
1.35                                                   .  = 

59.86 
59.80 

15.54 
10.35 

1.80 
51.1 
0  93 

0  016 

Percentage  of  the  sulphur  in  the  coal 
left  in  the  coke.                                  = 

48  8 

Coal  No.  11  shows  66.7  per  cent  of  washed  coal  containing 
6.48  per  cent  ash  and  87.3  per  cent  of  washed  coal  with  7.83  per 
cent  ash  as  against  10.81  per  cent  in  the  original  coal.  The 
washed  coal  in  both  tests  shows  a  material  reduction  in  the 
amount  of  sulphur  present.  Coal  No.  29  shows  85.5  per  cent  of 
washed  coal  with  6.16  per  cent  ash  and  1.14  per  cent  sulphur. 
The  coke  from  this  washed  coal  runs  10.35  per  cent  ash  and  0.93  per 
cent  sulphur,  which  indicates  the  possibility  of  production  of 
high  grade  coke  from  some  Ohio  coals.  For  further  details  of 
washing  tests  on  coal  see  Bulletin  No.  9  of  the  Ohio  Geological 
Survey,  also  Bulletin  No.  5  of  the  U.  S.  Bureau  of  Mines,  Depart- 
ment of  the  Interior. 


CHAPTER  VIII 
PURCHASE  OF  COAL  UNDER  SPECIFICATIONS 

Total  heating  value  as  an  index  of  the  commercial  value. 

As  has  previously  been  stated  under  the  heading  of  "The  com- 
mercial value  of  coal,'r  other  things  being  equal,  the  value  of  coals 
of  similar  composition  is  proportional  to  the  total  calories  or 
British  thermal  units  which  a  unit  of  the  coal  contains.  The 
value  of  different  coals  may  conveniently  be  compared  by  deter- 
mining how  many  large  calories  or  British  thermal  units  are 
obtained  for  one  cent  or  how  much  one  million  heat  units  cost  for 
each  of  the  several  coals. 

For  example,  suppose  the  price  asked  for  coal  (A)  is  $2.50 
per  ton  of  2000  pounds  with  a  heating  value  of  12,200  B.t.u. 
and  the  price  asked  for  coal  (B)  is  $2.25  per  ton  with  11,500 
B.t.u.  The  cost  of  1,000,000  B.t.u.  for  each  of  the  coals  is  as 
follows  : 


Other  factors  affecting  the  value  of  coal.  The  style  of  fur- 
nace, draft,  smoke  producing  qualities  of  the  coal  and  comparative 
amounts  of  ash  and  sulphur  are  additional  factors  which  may 
have  to  be  considered  in  determining  what  is  the  best  and  cheap- 
est coal.  No  definite  rule  can  be  laid  down  to  govern  some  of 
these  points.  The  experience  of  the  engineer  in  charge  of  the 
plant  or  the  experience  of  a  consulting  engineer  who  is  an  expert 
along  these  lines  is  perhaps  the  best  guide  as  to  what  is  likely 
to  be  the  best  fuel  for  the  particular  plant.  In  general,  the  higher 
the  moisture,  ash  and  sulphur  the  more  objectionable  the  coal, 

126 


PURCHASE  OF  COAL    UNDER  SPECIFICATIONS     127 

Actual  boiler  tests  upon  the  fuel   are  sometimes  necessary  to 
determine  what  fuel  is  the  best  for  a  particular  plant. 

Advantages  and  disadvantages  in  purchasing  coal  under 
specifications.  In  the  consideration  of  the  purchase  of  coal 
under  specifications  some  of  the  points  to  be  noted  are  as  follows: 

(1)  Where  the  consumer  buys  direct  from  the  operator  who 
handles  coal  from  a  certain  definite  locality  and  of  a  quality 
known  by  experience  to  be  satisfactory,  the  advantage  in  pur- 
chasing under  specifications  based  on  analysis  and  heating  value 
may  not  be  worth  the  extra  expense  involved  in  sampling  and 
analyzing  the  coal. 

(2)  In  markets  where  the  coal  supply  is  varied  and  where  it 
is  sold  under  trade  names  which  may  be  uncertain  or  misleading, 
large  buyers  should  be  able  to  buy  coal  to  better  advantage 
under  specifications  based  on  analysis  and  heating  value. 

(3)  Some  advantages  in  the  purchase  of  coal  under  specifica- 
tions are: 

(a)  Guards  against  delivery  of  poor  and  dirty  coal. 
(6)  Prevents  disputes  arising  from  the  condemnation  of  the 
coal  based  on  its  physical  appearance. 

(c)  Places   bidders  on  a  strictly  competitive  basis  as  to  the 

price  and  the  quality. 

(d)  Broadens  the  field  for  obtaining  coal  by  ignoring  trade 

names  and  making  moisture,  ash,  sulphur  and  heating 
value  the  basis  of  bids. 

(e)  The  analytical  results  and  heating  values  of  the  samples 

which  serve  as  a  basis  of  settlement  also  afford  a  ready 
check  upon  the  manner  in  which  the  coal  is  being 
burned. 

(4)  The  purchase  of  coal  under  specifications  involves  con- 
siderable expense  in  the  sampling  of  the  coal  and  in  the  analysis 
of  the  samples.     This  expense  adds  to  the  price  of  the  coal  and 
for  small  consumers  may  increase  the  cost  to  such  an  extent  as 
to  make  the  purchase  under  specifications  unprofitable.     When 
large  quantities  of  fuel  are  used,  the  expense  of  sampling  and 
analysis  figured  per  ton  of  coal  should  be  so  small  that  any  decided 
improvement  in  the  quality  of  the  coal  should  more  than  offset 
this  expense.    This  reduction  in  expense  per  ton  is  accomplished 
by  combining  the  samples  from  a  number  of  cars  so  that  each 
laboratory  sample  analyzed  may  represent  from  5  to  15  cars  of 


128  COAL 

coal.  The  sampler  and  chemist  must  necessarily  use  precautions 
in  combining  the  different  samples  into  one  sample  for  analysis. 
Especial  care  must  be  taken  to  avoid  moisture  losses  and  to  see 
that  the  portion  of  each  sample  taken  is  proportional  to  the 
tons  of  coal  it  represents. 

Specifications.  In  drawing  up  specifications  for  the  purchase 
of  coal  some  of  the  points  to  be  considered  are  as  follows: 

(1)  The   specifications   for   ash,    sulphur   and   heating   value 
should  be  adapted  to  the  grades  of  coal  which  are  available  and 
should  be  sufficiently  wide  in  their  range  as  to  enable  all  dealers 
in  suitable  grades  of  coal  to  submit  bids. 

(2)  The  negative  value  of  ash  in  coal,  due  to  extra  expense 
in  handling  the  ash  and  greater  trouble  to  operate  the  fire  together 
with  the  possible  lower  efficiency  should  be  taken  into  consider- 
ation.    The   United   States   Government   counts   this   negative 
value  at  two  cents  per  ton  for  each  per  cent  of  ash  above  the 
standard  ash  established  for  a  particular  specification. 

For  example,  in  comparing  the  bids  on  the  following  coals: 
Aj  bid  $2.20  a  ton,  heating  value  12,000  B.t.u.  and  ash  8  per  cent; 
B,  bid  $2.25  a  ton,  heating  value  12,100,  ash  7  per  cent.  Taking 
the  lower  ash — 7  per  cent — as  the  standard,  the  1  per  cent  excess 
of  ash  in  A  is  regarded  as  equivalent  to  2  cents  more  per  ton 
on  the  bid  price,  hence  the  bid  price  for  A  is  raised  to  $2.22  per 
ton  before  the  estimation  of  the  cost  per  million  B.t.u.  is  made. 
On  these  two  coals  with  this  change  for  ash  the  cost  per  million 
B.t.u., 

For  A  _*2.22X  1,000,000 _ 

12,000X2000 

"V 

$2.25X1,000,000 
"12^60X2000 

(3)  Payment  for  the  coal  is  based  upon  the  amount  of  coal 
weighed  and  the  sample  should  be  taken  at  the  time  of  weighing. 
The  precautions  to  prevent  moisture  loss  in  the  sample  have 
been  given  in  detail  under  "  Sampling." 

(4)  Payment  for  the  coal  is  based  on  the  coal  "  as  received  " 
and  specifications  for  bids  should  require  that  B.t.u.  be  on  the 
coal  "  as  received  "  rather  than  on  the  "  dry  coal." 

(5)  For  comparative  purposes  it  is  more  convenient  to  have 


PURCHASE  OF  COAL   UNDER  SPECIFICATIONS    129 

the  ash  expressed  on  the  "  dry  coal  "  basis.  This  involves  the 
use  of  a  double  standard  of  B.t.u.  on  the  "  coal  as  received  " 
and  of  ash  on  the  "  dry  coal."  The  Government  specifications 
for  bituminous  coals  are  on  this  double  standard. 

(6)  Ash  in  the  "  dry  coal  "  can  be  determined  at  any  time 
from  analysis  of  a  given  sample  of  the  coal,  but  the  B.t.u.  of  the 
coal  as  delivered  or  the  actual  amount  of  dry  coal  in  a  shipment 
can  only  be  determined  b.    the  taking  of  a  sample  at  the  time 
of  delivery,  as  the  amount  of  any  moisture  variation  in  the  coal 
after  weighing  cannot  be  determined  unless  comparison  is  made 
with  the  analysis  of  the  sample  taken  at  the  time  of  weighing. 

(7)  Premiums  or  bonuses  should  be  allowed  if  the  coal  is  better 
than  specifications  and  a  penalty  should  be  exacted  if  the  coal 
is  lower  in  heating  value  or  higher  in  ash  than  specifications. 
Some  objections  to  a  premium  or  bonus  are: 

(a)  Municipalities  may  in  some  cases  be  prohibited  by  law 

or  charter  from  paying  a  bonus.  This  is  hardly  an 
objection  to  the  principle,  though  it  may  prevent  its 
operation  in  special  cases. 

(b)  The  cost  of  the  coal  may  be  increased  by  having  to  pay 

a  bonus.  This  seems  hardly  a  valid  objection  as  if 
the  purchaser  gets  a  better  grade  of  coal  he  certainly 
should  be  expected  to  pay  for  it;  and  on  the  other  hand 
if  he  fails  to  get  a  good  grade  of  coal  he  is  entitled  to 
pay  for  just  what  he  gets  and  should  demand  a  penalty 
of  the  seller.  Bonuses  and  penalties  are  vital  items 
in  the  purchase  based  on  analytical  results  and  heating 
value  and  the  author  believes  that  the  test  of  time 
will  prove  the  soundness  of  the  principle  involved  and 
the  practicability  of  its  operation. 

(8)  The  contract  should  contain  provisions  for  insuring  regular 
delivery  of  the  coal  and  for  insuring  its  quality  to  within  certain 
prescribed  allowable  variations. 

Reports  from  twenty  cities  purchasing  coal  under  specifications 
given  in  the  Municipal  Journal,  Vol.  32,  p.  350-351,  are  very 
favorable  to  the  system.  One  report  indicates  a  saving  of  25 
per  cent,  others  10  per  cent.  Some  call  special  attention  to 
a  much  more  satisfactory  supply  of  coal. 

Abstracts  of  the  specifications  of  some  of  the  cities  are  as 
follows : 


130  COAL 

New  York  City.  The  B.-t.u.  standard  per  pound  dry  coal 
for  broken  coal  is  13,200  to  12,000  for  buckwheat  No.  3.  The 
ash,  11  per  cent  in  broken  coal  to  19  per  cent  in  buckwheat  No. 
3.  The  volatile  combustible  matter  is  8  per  cent  maximum  and 
volatile  sulphur  1.5  per  cent.  Moisture  is  4  per  cent  for  broken 
coal  to  6  per  cent  for  buckwheat  No.  3.  If  the  moisture  is  in 
excess  of  the  limit,  the  gross  weight  of  the  coal  is  corrected  by  an 
amount  directly  in  proportion  to  such  excess  of  moisture,  that 
is,  with  2  per  cent  excess  moisture  the  gross  weight  of  the  coal  is 
reduced  by  2  per  cent.  After  this  reduction  the  weight  is  reduced 
by  1  per  cent  for  each  per  cent  of  ash  in  excess  of  the  standard. 
The  gross  weight  after  correction  for  excess  moisture  is  reduced 
by  1  per  cent  for  each  100  B.t.u.  below  the  standard,  5  per  cent 
for  each  1  per  cent  of  volatile  sulphur  in  excess  of  the  standard, 
2  per  cent  for  each  1  per  cent' volatile  combustible  matter  in 
excess  of  the  standard.  Payment  is  made  on  the  gross  weight 
less  the  deductions  as  described. 

Cleveland.  The  standard  calorific  value  for  all  coal  is  13,005 
B.t.u.,  and  moisture  is  not  to  exceed  3  per  cent,  ash  13  per  cent 
or  sulphur  3.5  per  cent.  The  price  per  ton  of  coal  is  increased 
above  or  reduced  below  the  contract  price  according  as  the 
heating  value  is  more  or  less  than  the  standard,  the  increase  being 
1J  cents  per  ton  for  each  100  B.t.u.  up  to  13,900  and  2  cents  per 
ton  between  13,900  and  15,000,  remaining  constant  at  2.6  cents 
for  all  over  15,000.  Reduction  at  the  rate  of  1J  cents  per  ton 
down  to  12,600,  2  cents  per  ton  from  12,600  to  12,000,  3  cents 
per  ton  from  12,000  to  11,000,  4  cents  per  ton  from  11,000  to 
10,000  and  the  constant  amount  of  $1.00  where  the  heat  units 
fall  below  10,000. 

Toronto.  13,000  B.t.u.  is  taken  as  the  standard,  10  per  cent 
ash,  2  per  cent  moisture  and  1 J  per  cent  sulphur.  If  coal  delivered 
shows  a  lower  heating  value  than  the  standard,  the  city  may  reject 
or  accept  it,  the  amount  paid  in  the  latter  case  being  "  such  a  re- 
duced price  as  shall  make  the  uniform  coal  equal  in  heating  value 
to  the  city  to  the  contract  grade,"  and  there  shall  be  deducted 
from  the  contractor's  price  for  such  coal  a  proportionate  amount; 
and  if  the  coal  shall  show  a  higher  heating  value  than  specified 
the  contractor  shall  receive  a  proportionate  allowance. 

Norfolk.  The  standard  is  14,500  B.t.u.,  2J  per  cent  moisture, 
7  J  per  cent  ash,  1  per  cent  volatile  sulphur  and  22  per  cent  volatile 


PURCHASE  OF  COAL   UNDER  SPECIFICATIONS    131 

combustible  matter,  but  a  bidder  may  submit  a  proposition  for 
coal  of  a  different  standard.  If  a  coal  delivered  shows  moisture, 
ash,  sulphur  and  volatile  combustible  matter  in  excess  of  require- 
ments the  price  is  to  be  fixed  by  arbitration,  the  contractor  and 
the  city  each  appointing  one  arbitrator  and  these  two  selecting 
a  third.  The  gross  tonnage  of  the  coal  is  reduced  at  the  rate  of  1 
per  cent  for  each  100  B.t.u.  below  or  increased  1  per  cent  for 
each  100  B.t.u.  above  the  standard  analysis. 

Grand  Rapids.  The  city  requires  that  the  heating  value  per 
pound  of  dry  coal  be  stated  by  the  bidder  and  if  calorimeter 
tests  show  the  coal  to  fall  below  this  standard  a  rebate  is  made 
from  the  contract  price  and  an  increase  if  the  coal  comes  above 
the  standard,  the  rebate  or  increase  being  made  in  exact  propor- 
tion to  the  B.t.u.  For  instance,  if  the  bidder  guarantees  15,000 
B.t.u.  per  pound  and  the  coal  contains  only  14,000  the  contractor 
would  receive  yf  of  the  contract  price.  Any  coal  which  shows 
more  than  5  per  cent  less  heat  units  than  the  fixed  standard  may 
be  rejected.  Standards  are  established  for  different  kinds  of  coal 
varying  between  the  limits  of  15,000  to  11,000  B.t.u.,  a  minimum 
of  44  to  71  per  cent  fixed  carbon,  a  maximum  of  15  to  6  per  cent 
ash  and  a  maximum  of  3  to  f  per  cent  sulphur. 

Details  of  the  purchase  of  coal  by  the  United  States  Govern- 
ment under  specifications  together  with  the  form  of  specifica- 
tions, proposals,  guarantees,  contracts,  bonds,  etc.,  are  given 
in  Bulletin  41  of  the  United  States  Bureau  of  Mines. 


CHAPTER  IX 

ANALYSIS  OF  FLUE  GASES 

Composition  of  flue  gas.  Flue  gas  consists  of  carbon  dioxide 
(CO2),  oxygen  (62),  nitrogen  (%),  small  amounts  of  carbon 
monoxide  (CO),  and  small  amounts  of  sulphur  dioxide  (862), 
and  sometimes  probably  traces  of  hydrogen  (H2)  and  hydro- 
carbons The  gas  also  contains  water  vapor  but  in  ordinary  flue 
gas  analysis  the  water  vapor  is  not  considered,  as  the  analysis  is 
made  on  the  basis  of  dry  gas.  In  technical  analysis,  usually 
only  the  carbon  dioxide,  oxygen,  and  carbon  monoxide  are  deter- 
mined, the  remaining  gas  being  considered  as  nitrogen. 

Analysis  of  the  gas.  In  making  the  analysis  a  measured 
volume  of  the  gas  is  treated  successively  with  a  series  of  reagents 
that  absorb  the  several  constituents,  the  volume  remaining  being 
read  after  each  absorption.  The  measurement  of  the  gas  is  made 
in  a  graduated  tube  or  burette  which  should  be  surrounded  by 
a  water  jacket  to  insure  constant  temperature  during  the  time 
of  the  analysis.  The  measurements  of  the  gas  are  all  done  at 
atmospheric  pressure  and  as  the  time  of  making  analyses  is  short, 
it  is  assumed  that  the  barometer  remains  constant  during  that 
period,  while  the  use  of  the  water  jacket  should  prevent  any 
appreciable  temperature  changes.  However,  a  thermometer 
hung  in  the  water  jacket  is  a  decided  advantage  if  the  apparatus 
is»exposed  to  draughts  of  air  or  in  a  room  where  the  temperature 
varies. 

Sampling  the  gas.  The  tubes  best  adapted  for  sampling 
depend  upon  the  particular  conditions  under  which  the  sample 
has  to  be  taken.  In  collecting  samples  at  very  high  temperatures, 
1500  to  1600°  C.  (2700  to  2900°  F.)  a  quartz  tube  is  perhaps  the 
best  means  of  obtaining  a  sample.  Such  a  tube  stands  high 
temperatures  and  has  no  action  on  the  gas.  It  is  somewhat  expen- 
sive and  must  be  handled  with  care  to  prevent  breakage  bills 
becoming  excessive.  In  sampling  at  these  high  temperatures 

132 


ANALYSIS  OF  FLUE  GASES 


133 


the  tube  is  inserted  and  removed  at  the  taking  of  each  sample. 
If  the  tube  is  allowed  to  remain  in  the  furnace,  slag,  etc.,  soon 
destroy  it.  In  sampling  at  temperatures  from  400  to  800°  C. 
(750  to  1500°  F.)  water  jacketed  iron  tubes  permanently  installed 
during  the  period  of  the  test  are  satisfactory.  Sufficient  water 
must  be  used  to  insure  proper  cooling  if  entirely  satisfactory 
results  are  desired.  (See  Fig.  7.) 

A  disadvantage  of  the  quartz  and  water  jacketed  tubes  just 
described  is  that  the  sample  drawn  is  from  only  one  portion  of 
the  furnace  and  does  not  necessarily  represent  the  average  of 
the  gas  coming  off  at  that  time.  Shifting  the  end  of  the  tube  to 

SAMPLING    TUBE: 


WATER -JACKETED    SAMPLING  TUBE 


FIG.  7. — Sampling  Tubes. 

different  portions  of  the  furnace  during  a  series  of  tests  partially 
eliminates  error,  but  cannot  be  regarded  as  entirely  satisfactory. 
Sampling  gas  from  boiler  flues.  As  a  rule,  the  temperature 
of  the  gas  from  a  boiler  flue  is  considerably  below  330°  C.  (625°  F.) 
and  at  temperatures  less  than  this,  an  ordinary  iron  sampling 
tube  may  be  used.  (See  Fig.  7.)  The  tube  should  cross  the  flue 
at  a  right  angle  and  extend  to  within  6  inches  of  the  further  wall. 
The  end  of  the  tube  is  closed  with  a  cap  and 'along  the  lower 
side  of  the  tube  are  a  number  of  small  holes  ^  inch  in  diameter 
distributed  at  regular  intervals  of  6  inches  apart.  The  last  hole 
should  be  not  less  than  6  inches  from  the  near  wall  of  the  flue. 
The  diameter  of  the  holes  given  as  -^  inch  is  based  on  the  use  of 
a  pipe  not  less  than  1  inch  in  diameter.  If  the  holes  are  too  large 


134  COAL 

in  proportion  to  the  diameter  of  the  pipe,  too  much  of  the  gas 
will  enter  through  the  holes  which  are  nearest  to  the  aspirator. 

Aspiration  of  the  gas.  During  a  test,  gas  should  be  drawn 
continuously  from  the  flue  by  means  of  a  steam  or  water  aspira- 
tor. The  gas  should  be  passed  through  a  bottle  (about  16-oz.) 
filled  with  absorbent  cotton  to  filter  out  the  dirt  and  should  bubble 
through  water  in  a  second  bottle.  (See  Fig.  8.)  The  use  of  the 
water  bottle  is  to  enable  the  operator  to  ascertain  the  rate  and 
regularity  of  the  aspiration.  In  connecting  the  sampling  tube 
to  the  bottles  and  Orsat  apparatus,  rubber  tubes  should  be  avoided 
as  much  as  possible.  Any  long  length  of  pipe  or  tube  should  be 
of  iron  or  lead  with  only  short  rubber  connections  at  the  joints. 
All  rubber  connections  should  be  well  wired  and  the  apparatus 
tested  for  leaks  by  closing  the  stop  cock  on  the  sampling  tube 
and  noting  whether  the  aspiration  of  gas  continues  for  any  length 
of  time  or  whether  it  ceases  to  bubble  through  the  water  as  soon 
as  a  partial  vacuum  is  produced.  If  any  leaks  are  discovered 
they  must  be  stopped,  otherwise  air  will  be  introduced  into  the 
gas  analyzed  and  give  incorrect  results. 

Apparatus  for  making  the  analysis.  Some  form  of  Orsat 
apparatus  is  very  generally  used  in  making  the  flue-gas  deter- 
minations. A  typical  one  is  shown  in  Fig.  8.  This  differs  from 
most  of  those  sold  by  dealers  in  that  the  absorption  pipettes  are 
connected  at  the  rear  to  a  tube  connecting  to  the  two  bottles 
below,  which  form  a  water  seal  protecting  the  reagents  from  the 
action  of  the  air.  The  ordinary  Orsat  apparatus  as  furnished 
by  the  supply  houses  has  small  thin  rubber  bags  for  attaching 
to  the  rear  of  the  absorption  pipettes  but  these  soon  rot  and  leak 
and  are  generally  not  so  satisfactory  as  the  water  bottles  which 
are  permanent  and  need  only  to  have  the  rubber  tube  connections 
renewed  occasionally. 

Operation  of  the  Orsat  Apparatus.  Sufficient  water  is  poured 
into  the  levelling  bottle  so  that  when  the  three-way  cock  is  opened 
and  the  bottle  raised,  the  gas  will  escape  and  the  water  fill  the 
burette  to  a  point  in  the  capillary  tube.  A  few  drops  of  sulphuric 
acid  and  a  piece  of  litmus  paper  should  be  added  to  the  water 
in  the  levelling  bottle  in  order  to  insure  against  an  alkaline  reac- 
tion. The  adjustment  of  the  level  of  the  reagents  in  the  absorp- 
tion pipettes  to  a  fixed  point  in  the  capillary  tube  is  best  made 
as  follows:  The  stop-cock  to  each  of  the  absorption  pipettes 


ANALYSIS  OF  FLUE  GASES 


135 


being  closed,  the  3-way  cock  is  opened  to  the  air  and  the  levelling 
bottle  lowered  sufficiently  to  draw  in  25  to  30  c.c.  of  air.     The 


FIG.  8. — Orsat's  Apparatus. 

3-way  cock  is  then  closed.     Now,   holding  the  levelling  bottle 
high  enough  so  that  the  air  is  under  some  pressure,  the  stop- 


136  COAL 

cock  to  the  first  pipette  is  opened.  Some  air  will  rush  over  and 
the  level  of  the  liquid  will  be  lowered.  The  levelling  bottle 
is  then  gradually  lowered  until  the  liquid  in  the  absorption  pipette 
begins  to  rise.  The  lowering  of  the  levelling  bottle  is  continued 
gradually  until  the  liquid  in  the  absorption  pipette  reaches  the 
mark  on  the  capillary.  The  stop-cock  is  then  closed.  The  level- 
ling of  the  reagents  in  the  other  pipettes  is  done  in  the  same 
manner. 

This  method  of  levelling  prevents  the  suction  of  any  of  the 
reagents  up  into  the  capillary  tubes.  The  author  prefers,  in  using 
the  apparatus,  that  the  marked  point  on  the  capillary  of  the 
absorption  pipette  be  placed  considerably  below  the  stop-cock 
(in  the  apparatus  shown  in  Fig.  8,  the  marks  are  below  the 
rubber  connections  rather  than  above  them).  This  position 
of  the  mark  on  the  capillary  greatly  diminishes  the  danger  of 
allowing  the  reagent  to  pass  up  into  the  stop-cock  and  above  and 
while  a  little  more  residual  gas  is  left  in  the  capillaries,  in  a  series 
of  analyses  any  individual  errors  so  introduced  are  eliminated 
in  the  average  of  the  series. 

Drawing  a  sample  into  the  Orsat  apparatus.  If  the  burette 
is  not  completely  filled  with  water,  it  is  filled  by  raising  the  level- 
ling bottle  and  opening  the  3-way  cock  to  the  air  until  the  water 
enters  the  capillary.  The  cock  is  then  closed  and  the  levelling 
bottle  lowered.  If  the  apparatus  is  tight  the  level  of  the  water 
in  the  capillary  and  the  level  of  the  reagents  in  the  absorption 
pipettes  should  remain  constant.  If  any  leaks  are  present  they 
must  be  stopped  before  trying  to  make  an  analysis.  If  the  appara- 
tus is  tight,  the  3-way  stop-cock  is  turned  so  as  to  connect  the  gas 
burette  with  the  gas  bottles  through  which  the  gas  is  passing 
to  the  aspirator  and  the  pinch  cock  on  the  rubber  tube  (see  Fig. 
8),  is  opened  and  50  or  60  c.c.  of  gas  drawn  into  the  apparatus. 
The  pinch  cock  is  then  closed,  the  levelling  bottle  raised,  the  3- 
way  cock  opened  to  the  air,  and  the  gas  is  forced  out  of  the  appara- 
tus till  the  water  again  enters  the  capillary.  This  preliminary 
drawing  of  gas  is  essential  in  order  to  fill  the  capillaries  and 
rubber  tube  with  gas  having  approximately  the  same  composi- 
tion as  the  sample  to  be  analyzed. 

With  the  levelling  bottle  lowered,  the  3-way  cock  is  again 
opened  to  the  gas  supply,  the  pinch  cock  again  opened  and  gas 
drawn  in  until  over  100  c.c.  are  obtained.  The  pinch  cock  and 


ANALYSIS  OF  FLUE  GASES  137 

3-way  cock  are  then  closed.  The  levelling  bottle  is  raised  until 
the  gas  in  the  burette  reads  zero.  The  rubber  tube  connecting 
the  levelling  bottle  to  the  burette  is  then  pinched  with  the  thumb 
and  finger  and  the  3-way  cock  opened  to  the  air  to  allow  the  excess 
of  gas  to  escape.  The  cock  is  then  closed,  the  levelling  bottle 
adjusted  and  the  reading  of  the  gas  noted.  It  should  read  zero 
or  at  most  0.1  or  0.2  c.c.  above  zero.  The  actual  reading  is 
recorded,  the  levelling  bottle  raised  and  the  gas  run  over  into 
the  first  absorption  pipette  containing  the  potassium  hydroxide 
solution.  The  cock  is  closed  and  the  gas  allowed  to  remain  in  the 
pipette  for  about  a  minute.  It  is  then  run  back  into  the  burette, 
the  levelling  bottle  adjusted  and  a  reading  taken.  A  second 
absorption  in  the  potassium  hydroxide  pipette  is  then  made  and 
a  second  burette  reading  taken.  This  reading  should  check  the 
first  one.  If  not,  a  third  absorption  is  necessary.  The  difference 
between  the  initial  readings  and  the  reading  after  absorption  in 
the  potassium  hydroxide  pipette  equals  the  percentage  of  carbon 
dioxide.  The  gas  is  next  run  into  the  pyrogallic  acid  pipette  and 
run  back  and  forward  several  times  before  a  reading  is  made. 
After  a  reading  it  is  again  run  back  and  forward  several  times 
and  a  second  reading  taken.  The  absorption  and  readings  are 
continued  until  the  last  two  readings  agree  exactly.  The  difference 
between  the  final  reading  from  pyrogallic  acid  absorption  and  the 
absorption  in  the  potassium  hydroxide  pipette  equals  the  per- 
centage of  oxygen  present.  The  determination  of  carbon  mon- 
oxide is  made  in  a  similar  manner  by  running  the  residual  gas 
into  the  cuprous  chloride  pipette  and  allowing  it  to  stand  for  some 
little  time.  The  absorption  is  continued  until  two  readings 
check.  The  difference  between  the  reading  from  the  pyrogallic 
acid  pipette  and  the  reading  after  the  absorption  by  cuprous 
chloride  equals  the  percentage  of  carbon  monoxide  present, 
provided  that  all  of  the  oxygen  had  been  completely  absorbed, 
as  any  oxygen  not  taken  out  by  the  pyrogallic  acid  pipette  is 
taken  up  by  the  cuprous  chloride  and  hence  counts  as  carbon 
monoxide. 

In  beginning  a  series  of  analyses  it  is  necessary  to  draw  several 
preliminary  samples  oi  the  flue  gas  in  order  to  saturate  the  water 
in  the  burette  with  the  gases  being  analyzed.  Otherwise,  the  first 
few  results  will  be  too  low  due  to  the  absorption  of  the  gas  in 
the  water. 


138  COAL 


REAGENTS  USED  AND  THEIR  PREPARATION 

For  absorbing  carbon  dioxide  (CC>2)  a  25  per  cent  solution  of 
potassium  hydroxide  is  used.  For  absorbing  oxygen  (62)  an 
alkaline  solution  of  pyrogallic  acid  is  generally  used.  For  absorbing 
carbon  monoxide  (CO)  an  acid  or  ammoniacal  solution  of  cuprous 
chloride  is  used.  The  preparation  of  these  reagents  is  as  follows: 

Potassium  hydroxide  (KOH)  solution.  Dissolve  100  grams  of 
the  best  quality  potassium  hydroxide  in  300  grams  of  water. 
Let  the  solution  stand  in  a  closed  bottle  till  any  oxide  of  iron 
settles  and  use  only  the  clear  solution.  If  many  analyses  are  to 
be  made  it  is  best  to  prepare  a  large  quantity  of  this  solution  and 
keep  it  ready  for  use. 

Pyrogallic  acid  solution.  The  white  re-sublimed  acid  should 
be  used.  In  ordinary  flue  gas  analysis  15  grams  of  pyrogallic 
acid  are  dissolved  in  150  c.c.  of  the  25  per  cent  potassium  hydroxide 
solution,  the  solution  of  the  pyrogallic  acid  being  made  at  the 
time  the  Orsat  apparatus  is  filled. 

Cuprous-ammonium  chloride  solution.  This  is  prepared 
as  follows :  250  grams  of  ammonium  chloride '  are  dissolved  in 
750  c.c.  of  water  in  a  bottle  provided  with  a  good  rubber  stopper 
and  200  grams  of  cuprous  chloride  are  added.  The  latter  on  « 
frequent  agitation  dissolves,  leaving  a  little  cupric  oxychloride 
behind,  forming  a  brown  liquid  which  keeps  for  an  indefinite 
time,  especially  if  a  copper  spiral  long  enough  to  reach  from  the 
top  to  the  bottom  of  the  solution  is  inserted  into  the  bottle.  In 
contact  with  air  the  solution  forms  a  precipitate  of  green  cupric 
oxychloride.  In  order  to  make  it  ready  for  use,  it  is  mixed  with 
one-third  its  volume  of  ammonia,  specific  gravity  0.910. 

Acid  cuprous  chloride  solution.  To  prepare  125  c.c.  of  solution 
the  process  is  as  follows :  12  grams  of  pulverized  and  recently  ignited 
cupric  oxide  (CuO),  are  dissolved  in  125  c.c.  of  concentrated  hydro- 
chloric acid.  Next  40  grams  of  crystallized  copper  sulphate 
(CuSO45H2O)  are  dissolved  in  about  200  c.c.  of  water,  adding 
a  few  drops  of  sulphuric  acid.  To  this  solution  are  added  12  grams 
of  granular  or  mossy  zinc  which  is  added  carefully  to  avoid  violent 
effervescence.  This  zinc  may  be  added  to  the  copper  sulphate 
solution  before  the  copper  sulphate  has  entirely  dissolved.  The 
zinc  precipitates  the  copper  as  a  brown  powder  and  the  excess  of 
zinc  is  dissolved  in  the  sulphuric  acid  more  of  which  is  added 


ANALYSIS  OF  FLUE  GASES  139 

if  necessary  to  complete  the  solution.  The  liquid  is  then  decanted 
closely  and  washed  by  decant ation  till  free  from  zinc  sulphate. 
The  precipitated  copper  is  then  transferred  to  a  small  flask  (about 
150  c.c.  capacity)  and  the  water  used  in  transferring  poured  off 
as  completely  as  possible.  The  solution  of  the  cupric  oxide  in 
hydrochloric  acid  is  then  added  to  the  flask  which  is  stoppered 
loosely  and  shaken  occasionally  until  the  solution  becomes  almost 
or  entirely  clear.  The  rapidity  of  reduction  may  be  increased 
by  dropping  into  the  flask  several  long  pieces  of  sheet  copper 
or  copper  wire  which  accelerate  the  reduction  of  the  upper  por- 
tion of  the  liquid.  After  the  solution  has  become  practically 
clear  it  is  either  transferred  at  once  to  the  absorption  pipette 
of  the  Orsat  apparatus  or  poured  into  a  stock  bottle  containing 
strips  of  metallic  copper.  The  solution  should  almost  fill  this 
stock  bottle  wrhich  must  be  well  stoppered. 

Filling  the  Orsat  apparatus.  The  old  solutions  in  the  absorp- 
tion pipettes  are  removed  by  forcing  air  from  the  gas  burette 
into  the  absorption  bulbs  and  forcing  the  liquid  into  the  rear 
bulbs.  Each  is  then  emptied  by  a  small  syphon  first  filled  with 
water  and  inserted  to  the  bottom  of  the  bulb.  The  first  rear  bulb — 
the  one  nearest  to  the  measuring  burette — is  then  filled  with  a 
proper  amount  of  potassium  hydroxide  solution.  To  fill  the  second 
bulb  with  pyro  solution  place  a  large  funnel  into  the  bulb  and  put 
into  it  12  grams  of  pyrogallic  acid.  This  is  then  washed  down  in 
to  the  bulb  with  120  c.c.  of  the  25  per  cent  potash  solution.  If 
this  amount  of  reagent  does  not  properly  fill  the  pipette  more  or 
less  potash  solution  should  be  taken  and  the  amount  of  pyrogallic 
acid  increased  or  reduced  proportionately.  The  filling  of  this 
pipette  should  be  done  as  quickly  as  possible  and  as  soon  as  filled 
it  should  be  stoppered  to  protect  from  the  action  of  the  air.  The 
third  bulb  is  filled  with  cuprous  chloride  solution,  the  proper 
amount  being  poured  into  the  pipette  as  quickly  as  possible 
and  the  pipette  stoppered  to  protect  the  reagent  from  the  air. 
The  stoppers  are  next  removed  from  the  absorption  bulbs  and  the 
stoppers  on  the  connections  to  the  water  sealed  bottles  securely 
pushed  into  place,  as  it  is  essential  that  there  be  no  leakage  if 
the  reagents  are  to  be  properly  protected  from  the  air. 

Absorbing  power  of  reagents.  100  c.c.  of  a  25  per  cent 
potassium  hydroxide  solution  will  quickly  and  completely  absorb 
500  or  600  c.c.  of  carbon  dioxide.  Theoretically  it  is  capable  of 


140  COAL 

absorbing  several  thousand  c.c.  but  practically  it  should  never  be 
used  to  any  where  near  its  theoretical  limit  and  it  is  advisable  to 
use  fresh  reagent  in  the  Orsat  apparatus  after  50  or  60  flue  gas 
determinations  have  been  made  as  the  loss  of  time  due  to  the  slow- 
ness of  the  absorption  of  carbon  dioxide  more  than  counter- 
balances the  slight  cost  for  new  reagent.  100  c.c.  of  the  alkaline 
pyrogallic  acid  solution  is  capable  of  absorbing  several  hundred 
c.c.  of  oxygen  and  if  the  reagent  is  kept  properly  protected  from 
the  air  the  Orsat  solution  should  easily  be  good  for  30  or  40  deter- 
minations of  oxygen.  However,  the  author  prefers  to  begin  each 
day's  work  with  an  Orsat  apparatus  with  a  new  solution  of  pyro- 
gallic acid,  as  any  slowing  up  in  the  absorption  by  an  old  solution, 
which  frequently  occurs  if  a  solution  is  used  a  second  day,  more 
than  makes  up  for  the  trouble  or  expense  of  renewing  the  solution 
each  day. 

100  c.c.  of  cuprous  chloride  solution  should  readily  absorb 
50  c.c.  of  carbon  monoxide.  However,  the  last  traces  are 
absorbed  very  slowly  or  not  at  all  by  a  solution  which  has 
previously  absorbed  very  much  carbon  monoxide,  and  the  author 
prefers  to  renew  the  cuprous  chloride  solution  in  the  Orsat 
apparatus  quite  frequently  even  though  the  actual  absorption 
during  the  tests  upon  which  it  has  been  used  do  not  total  up 
very  many  c.c. 

Care  of  apparatus.  In  setting  up  the  Orsat  apparatus,  the 
capillary  tubes  and  absorption  pipettes  should  be  washed  with 
dilute  hydrochloric  acid  and  then  rinsed  with  pure  water.  The 
ends  of  the  tubes  fitting  into  the  rubber  tube  connections  should 
be  coated  with  vaseline  and  the  connections  should  be  securely 
wired  to  prevent  leaks;  the  stop-cocks  should  be  well  lubri- 
cated with  vaseline  or  some  similar  lubricant.  In  cleaning 
out  an  old  solution  of  cuprous  chloride  it  is  sometimes  advis- 
able to  wash  out  the  cuprous  chloride  pipette  with  rather  strong 
hydrochloric  acid  to  dissolve  any  precipitated  cuprous  chloride 
which  cannot  be  removed  by  the  use  of  pure  water.  If  at  any 
time  any  reagent  gets  into  a  stop-cock  or  capillary  it  should  be 
at  once  flushed  out  with  water  and  if  necessary  the  apparatus 
disconnected  and  cleaned.  Before  putting  the  apparatus  away 
all  stop-cocks  should  be  loosened  slightly  and  given  an  applica- 
tion of  vaseline  if  needed.  If  the  apparatus  is  to  be  set  away  for 
any  great  length  of  time,  it  is  advisable  to  remove  the  stop-cocks 


ANALYSIS  OF  FLUE  GASES  141 

entirely  and  to  insert  a  narrow  strip  of  paper  into  eaeh  socket 
before  replacing  the  stop-cock.  These  strips  of  paper  are  perma- 
nent safe-guards  against  the  cocks  sticking,  as  is  frequently  the 
case  if  the  apparatus  is  set  away  without  any  care  being  given  to 
them.  The  gas  burette  should  be  left  filled  with  gas  or  air 
rather  than  with  water  so  that  if  any  leak  develops  there  can  be 
no  possibility  of  drawing  reagents  up  in  the  capillaries. 

DISCUSSION  AND  INTERPRETATION  OF  ORSAT  RESULTS 

These  may  perhaps  best  be  understood  by  discussing  the 
reactions  which  take  place  during  combustion  of  a  coal.  The 
average  analysis  of  a  number  of  samples  of  Ohio  No.  6  coal 
(Hocking  or  Middle  Kittanning  coal)  is  as  follows : 

Carbon 69.03 

Total  hydrogen 5 . 43 

Nitrogen 1 . 26 

Oxygen 13 . 62 

Sulphur 3 . 30 

Ash 7.36 

Available  hydrogen 3 . 73 

The  available  hydrogen  is  obtained  from  the  total  hydrogen 
by  subtracting  from  the  total  hydrogen  J  of  the  oxygen  in  the 
coal  =  5.43 -(-J-  of  13.62) -3.73.  The  reactions  for  complete 
combustion  of  this  coal  in  air  (air  =  by  volume  one  part  of  oxygen 
and  3.8  parts  of  nitrogen)  are  as  follows. 

C+O2+3.8  N2      =  C02+3.8  N2; 
2H2+02+3.8N2  =  2H20+3.8N2; 

S+02+3.8  N2       =SO2+3.8  N2; 

N2  =  N2. 

Gas  reactions  are  most  easily  handled  if  the  gases  produced 
are  figured  with  a  molecular  volume  as  the  unit  for  calculation. 
A  molecular  volume  of  gas  is  the  volume  which  the  molecular 
weight  of  the  gas  in  grams  occupies.  Under  standard  conditions, 
0°  C.  and  760  mm.  of  mercury  pressure,  this  =  22.4  liters  (0.79 
cu.ft.).  As  an  illustration,  the  molecular  weight  of  carbon  dioxide 
(CO2)  =44.  The  molecular  weight  of  carbon  monoxide  (CO)  =28. 
44  grams  of  carbon  dioxide  (CO2)  or  28  grams  of  carbon  monoxide 


142  COAL. 

(CO)  =22.4  liters  by  volume,  at  0°  C.  and  at  a  pressure  of  760  mm. 
of  mercury. 

1  molecular  volume  of  CO2  =  12  grams  of  carbon  or  0.01  gram 
carbon  =  0.000833  molecular  volume  of  CC^. 

1  molecular  volume  of  H20  =  2  grams  of  hydrogen  (H^)  or 
0.01  gram  of  hydrogen  =  0.005  molecular  volume  H2O. 

1  molecular  volume  of  SO2  =  32  grams  of  sulphur  or  0.01  gram 
of  sulphur  =  0.00031  molecular  volume  of  SO2. 

1  molecular  volume  of  N2  =  28  grams  of  N2  or  0.01  gram  of 
nitrogen  =  0.000357  molecular  volume  of  N2. 

From  these  relations  the  molecular  volumes  of  the  products 
of  complete  combustion  of  1  gram  of  coal  with  no  excess  air  are 
as  follows : 

For  the  carbon  to  C+O2+3.8N2  =  CO2+3.8N2  =  69.03  X 
0.000833  =  0.0575  molecular  volume  of  CO2+ (0.0575X3.8  = 
0.2185)  molecular  volume  N2. 

For  the  available  hydrogen  to  2H2+O2+3.8N2  =  2H2O+3.8N2 
=  3.73X0.005  =  0.01865  molecular  volume  H20  + 

3  8 
(0.01865 X— =  0.0354)  molecular  volume  N2. 

The  hydrogen  present  in  the  coal  in  the  form  of  water  =  J  the 
oxygen  in  the  coal  =  £  of  0.1362  =  0.0170  gram  of  hydrogen. 
This  hydrogen  to  2H2O  =  1.70X0.005  =  0.0085  molecular  volume 
H20. 

For  the  sulphur  to  S+02+3.8N2  =  SO2+3.8N2  =  3.30X0.00031 
=  0.001  molecular  volume  SO2+ (0.001X3.8  =  0.0038)  molecular 
volume  N2. 

For  the  nitrogen  in  the  coal  to  N2  =  1.26X0.000357  =  0.00045 
molecular  volume  of  N2. 

Collecting  together  the  nitrogen  from  the  air  required  for 
complete*  combustion,  0.2185+0.0354+0.0038  =  0.2577  molecular 
volume  of  nitrogen. 

If  100  per  cent  excess  air  be  assumed  the  nitrogen  in  this  100  per 
cent  excess  air  =  therefore  0.2577  molecular  volume  and  the  oxygen 

in  this  100  per  cent  excess  air  =  -      -  =0.0678  molecular  volume. 

0.0 

Collecting  these  values  for  the  products  of  combustion, 
allowing  the  100  per  cent  excess  of  air,  the  molecular  volumes  of 


ANALYSIS  OF  FLUE  GASES  143 

gas  from  the  complete  combustion  of  one  gram  of  coal  are   as 
follows : 

CO2  =  0.0575  molecular  volume 

O2  =  0.0678 

H2O  (vapor)    =  =  0.0271 

S02  =  0.0010 

N2  =  0.5158 


Total  molecular   volumes  =  0.6692  =  15.0  liters  at  0°  C.  and  760 
mm.  pressure. 

The  Orsat  analysis  of  the  gas  determines  only  the  carbon 
dioxide,  the  carbon  monoxide,  and  the  oxygen  present.  With 
complete  combustion  it  is  assumed  that  no  carbon  monoxide  is 
produced  and  the  analysis  has  only  to  do  with  carbon  dioxide  and 
oxygen,  the  difference  being  nitrogen.  The  sulphur  dioxide 
formed  during  combustion  amounts  by  volume  to  about  -gV  of  the 
volume  of  carbon  dioxide  and  a  small  portion  of  this  sulphur 
dioxide  may  be  absorbed  by  the  potassium  hydroxide  solution 
and  hence  count,  as  carbon  dioxide.  However,  it  is  altogether 
probable  that  the  greater  part  is  absorbed  in  the  water  in  the 
Orsat  apparatus  or  elsewhere  before  the  actual  carbon  dioxide 
determination  is  made  and  for  all  practical  purposes  the  volume 
of  the  sulphur  dioxide  in  the  Orsat  determination  may  be  neg- 
lected. The  excess  of  water  vapor  in  the  gas  condenses  and  the 
Orsat  gases  are  saturated  with  water  vapor  at  the  temperature  at 
which  they  are  analyzed.  With  no  change  in  temperature,  the 
proportion  of  water  vapor  present  during  an  analysis  remains 
unchanged  and  the  absorption  of  the  gas  by  the  potash  or  pyro- 
gallic  acid  or  cuprous  chloride  pipette  represents  the  percentage 
of  carbon  dioxide,  oxygen,  and  carbon  monoxide  present  in  the 
gas,  as  the  effect  of  the  presence  of  water  vapor  merely  diminishes 
the  pressure  of  the  residual  gas  analyzed,  but  it  has  no  effect 
on  its  relative  percentage  composition. 

Referring  to  the  reactions  given  (p.  141)  for  the  combus- 
tion of  the  Ohio  No.  6  coal,  for  one  gram  of  coal  burned 
there  are  present  in  the  flue  gas,  assuming  theoretical  combustion, 
50  per  cent  excess  air  and  100  per  cent  excess  air,  gases  as  fol- 
lows :  (H2O  vapor  and  SO2  are  omitted  from  the  tabulation  since 
they  do  not  enter  into  the  Orsat  analysis). 


144 


COAL 


Gas  Compo- 
sition. 

Theoretical  Combustion.   50  Per  Cent  Excess  Air. 

100  Per  Cent  Excess  Air. 

Mol.  Vol. 

Per  Cent. 

Mol.  Vol. 

Per  Cent. 

Mol.  Vol. 

Per  Cent. 

CO, 

o. 

N2 

0.0575 
0*2581 

18.22 

'81.78 

0.0575 
0.0339 
0.3870 

12.02 
7.09 
80.89 

0.0575 
0.0678 
0.5158 

8.98 
10.58 
80.44 

0.3156 

100.00 

0.4784 

100.00 

0.6411 

100.00 

The  effect  of  the  formation  of  carbon  monoxide  instead  of 
carbon  dioxide  is  to  lower  the  nitrogen  percentage  since  only  one- 
half  as  much  air  is  required  to  burn  carbon  to  carbon  monoxide 
as  is  required  to  burn  it  to  carbon  dioxide  and  less  residual  nitrogen 
remains  after  the  absorption  of  carbon  dioxide,  oxygen  and 
carbon  monoxide.  0.01  gram  of  carbon  to  CO  =  0.000833  molec- 
ular volume  of  CO  =  .00158  molecular  volume  of  N2  as  against 
0.00316  molecular  volume  of  N2  required  for  an  equivalent 
amount  of  carbon  to  CO2.  With  50  per  cent  excess  air  and 
0.01  gram  of  carbon  burned  to  CO  instead  of  CO2,  the  products 
of  combustion  of  1  gram  of  coal,  omitting  the  tabulation  of 
and  S02  are  as  follows; 


Mol.  Vol. 

CO2 0.0567 

O2- 0.0337 

CO 0.00083 

N2 0.3841 


0.4753 


Per  Cent. 

11.93 

7.09 

0.17 

80.81 

100.00 


The  higher  the  sulphur  and  the  available  hydrogen  the  more 
oxygen  is  required  for  combustion  and  the  greater  the  volume 
of  nitrogen  in  the  residual  gas.  0.01  gram  of  available  hydrogen 
requires  air  for  combustion  equivalent  to  0.0095  molecular  volume 
of  N£.  With  50  per  cent  excess  air  this  equals  0.0143  molecular 
volume  of  N2+0.0013  molecular  volume  of  02  =  0.0156  molecular 
volume  increase  in  the  residual  gas.  In  this  case,  assuming  the 
other  constituents  of  the  coal  to  remain  the  same,  the  products  of 
combustion  of  1  gram  of  this  coal  containing  4.73  per  cent  available 
hydrogen  (omitting  H^O  and  SO2  from  the  tabulation)  are  as 
follows: 


ANALYSIS  OF  FLUE  GASES  145 

Mol.  Vol.  Per  Cent. 

CO2 0.0575  11.64 

O2 0.0352  7.12 

N2..  0.4013  81.24 


0.4940  100.00 

With  50  per  cent  excess  air,  1  per  cent  more  of  available  hydro- 
gen raises  the  nitrogen  about  0.35  per  cent.  The  effect  of  sulphur 
is  about  I  as  great  as  the  effect  of  an  equal  weight  of  hydrogen 
or  an  increase  of  1  per  cent  in  sulphur  increases  the  nitrogen  by 
about  0.05  per  cent. 

With  100  per  cent  excess  air  present  the  effects  of  hydrogen 
and  sulphur  are  about  f  as  great  as  with  50  per  cent  excess  or 
approximately  0.24  for  the  hydrogen  and  0.03  for  the  sulphur. 
The  available  hydrogen  in  the  sample  calculated  is  3.73  per  cent 
and  an  increase  in  available  hydrogen  of  1  per  cent  higher  than 
this  amount  is  more  than  is  ever  actually  found.  Most  coals 
contain  less  than  4  per  cent.  On  the  basis  of  not  over  4  per  cent 
available  hydrogen  and  with  the  amount  of  carbon  corresponding 
to  that  usually  found  in  coals  high  in  available  hydrogen  and  with 
50  per  cent  excess  air  corresponding  to  approximately  12  per  cent 
of  carbon  dioxide  in  the  flue  gas,  the  nitrogen  'should  not  run 
above  81  per  cent.  With  larger  excess  air,  as  100  per  cent, 
corresponding  to  approximately  9  per  cent  of  the  carbon  dioxide 
in  the  flue  gas,  the  nitrogen  should  be  appreciably  less  than  81  per 
cent.  With  smaller  excess  air  and  higher  carbon  dioxide  and 
the  absence  of  carbon  monoxide,  the  nitrogen  may  possibly 
exceed  81  per  cent. 

The  effects  of  the  presence  of  unburned  hydrogen  should  be 
considered  as  to  its  relation  upon  the  Orsat  analysis  and  the  heat 
balance.  If  it  be  assumed  for  illustration  that  of  the  3.73  per 
cent  available  hydrogen,  one  part  escapes  as  free  hydrogen  and 
the  remaining  2.73  burn  to  water,  allowing  50  per  cent  excess  air, 
the  products  of  combustion  from  1  gram  of  coal  (omitting 
vapor  and  SOo  from  the  tabulation),  are  as  follows: 


CO2 

Mol.  Vol. 

0  0575 

Per  Cent. 

12  29 

02  

0.0326 
0.3727 

6.97 
79.67 

H2..     . 

0  .  0050 

1.07 

Total..  .  0.4678  100.00 


146  COAL 

Deducting  the  sum  of  the  carbon  dioxide  and  oxygen  (19.26) 
from  100  =  80.74  as  the  percentage  of  nitrogen  obtained.  This  is 
only  0.15  per  cent  lower  than  the  figure  obtained  for  complete 
combustion,  hence  as  far  as  any  visible  effects  in  the  Orsat  deter- 
mination are  concerned,  unburned  hydrogen  has  little  effect  upon 
the  totals  of  the  carbon  dioxide,  oxygen,  and  carbon  monoxide. 
A  failure  of  this  amount  of  hydrogen  to  burn  would  mean,  how- 
ever, a  loss  of  334  calories  or  5  per  cent  of  the  total  heat  in  the 
fuel. 

In  a  similar  way  it  may  be  shown  that  the  presence  of  large 
amounts  of  methane  in  the  gas  would  have  little  effect  upon  the 
percentage  result  obtained  for  nitrogen.  With  50  per  cent  excess 
air  and  assuming  0.01  gram  of  carbon  and  a  corresponding  amount 
(0.0033  gram)  of  hydrogen  remaining  as  methane  (CHU),  the 
products  of  combustion  of  1  gram  of  the  coal  (omitting  H^O  and 
SC>2  from  the  tabulation),  are  as  follows: 

Mol  Vol.  Per  Cent. 

CO2 0.0567  12.12 

O2..     , 0.0327  6.99 

N2 0.3776  80.71 

CH4  ..                             .  0.00083  0.18 


Total 0.46783  100.00 

The  sum  of  the  nitrogen  and  methane  equals  80.89  which  is 
the  same  as  the  value  for  nitrogen  assuming  complete  combustion 
and  50  per  cent  excess  air. 

The  above  calculations  may  serve  to  make  clear  why  the 
nitrogen  from-  different  determinations  is  not  a  fixed  quantity, 
and  also  that  the  value  obtained  for  nitrogen  is  not  necessarily 
all  nitrogen.  By  applying  similar  calculations  to  any  coal  for  any 
observed  or  assumed  set  of  conditions,  possible  and  probable  per- 
centages may  be  readily  calculated  and  may  serve  to  prove  or  dis- 
prove speculations  as  to  the  possible  or  probable  effects  of  unburned 
hydrogen,  carbon,  etc.  Such  calculations  usually  make  plain 
or  certain  the  fact  that  as  a  rule  irregular  determinations  cannot 
be  satisfactorily  explained  in  such  a  way  and  that  irregular 
results  are  more  probably  due  to  errors  of  manipulation,  leaks 
in  the  apparatus,  etc. 

Errors  in  the  Orsat  determination.  (1)  Leaks  in  the  appara- 
tus or  connections  leading  to  the  sampling  tube. 


ANALYSIS   OF  FLUE  GASES  147 

(2)  Errors  due  to  reagents  getting  into  the  apparatus,  espe- 
cially into  the  capillary  connecting  tube. 

(3)  Errors  in  levelling. 

(4)  Errors  due  to  insufficient  time  of  drainage  of  the  burette 
before  taking  a  reading. 

(5)  Use  of  old  reagents  and  failure  to  absorb  completely  tend 
to  give  low  results  for  carbon  dioxide,  low  results  for  oxygen,  high 
or  low  results  for  carbon  monoxide,  but  a  low  total  for  the  three. 

(6)  Errors  due  to  temperature  changes  during  a  determination. 
Nos.  1,  3,  4  and  5  need  no  special  comment,  except  to  call 

attention  to  possible  errors  from  these  causes. 

No.  2.  Any  absorption  of  oxygen  or  carbon  dioxide  by  traces 
of  potassium  hydroxide  or  pyrogallic  acid  solution  in  the  connect- 
ing tube  gives  of  course  too  low  a  result  for  oxygen  or  carbon 
dioxide  and  consequently  too  high  a  result  for  nitrogen.  Many 
high  nitrogens  are  probably  due  to  carelessness  in  this  particular. 

No.  6.  Errors  due  to  temperature  changes  during  a  determina- 
tion may  be  of  considerable  magnitude,  which  may  perhaps  best 
be  shown  by  a  particular  example.  Suppose  the  temperature 
of  the  gas  at  the  beginning  of  a  determination  =  20°  C.  At  the 
end  of  the  carbon  dioxide  absorption  =  20°  C.  At  the  end  of  the 
oxygen  absorption  =  21°  C.  and  at  the  end  of  the  carbon  monoxide 
absorption  =  22°  C.,  what  is  the  effect  upon  an  analysis,  the 
observed  readings  of  which  are  as  follows: 


Observed  Readings.  Observed  Per  Cent. 
Initial  readings          =   0.0 

CO2 10.00  10.00 

O2 19.00  9.00 

CO 19.00  0.00 

N2 81.00 


Since  there  is  no  temperature  change  during  the  carbon  dioxide 
determination  the  determined  percentage  of  carbon  dioxide  (10  per 
cent)  equals  the  true  percentage  present.  During  the  determina- 
tion of  oxygen  the  temperature  increases  one  degree  or  from  293 
degrees  absolute  to  294  degrees  absolute.  Hence  the  observed 
volume  of  residual  gas  (81  c.c.)  is  -g-gT  larger  than  the  volume  of 
the  gas  at  20°  C.  -gi^  of  81  =0.27  c.c.  or  the  corrected  volume 
of  the  residual  gas  is  80.73,  from  which  the  corrected  percentage 
of  oxygen  =  9.27  as  against  9.00  observed.  Likewise,  for  carbon 


148 


COAL 


monoxide,  the  observed  volume  81.00  at  22°  is  -jf-g-  larger  than  the 
volume  of  the  gas  at  20°  or  the  volume  of  the  residual  gas  cor- 
rected to  20°  C.  is  approximately  80.46  c.c.  and  the  corrected 
percentage  of  carbon  monoxide  is  0.27  instead  of  zero,  the  deter- 
mined percentage.  This  error  appears  large  enough  but  there 
is  still  another  effect  to  be  considered.  The  aqueous  tension 
of  the  water  vapor  of  the  gas  at  20°  C.  =  17.4  mm.  of  mercury, 
at  21°  C.  =  18.5  mm.  of  mercury,  at  22°  =  19. 7  mm.  of  mercury. 
Assuming  a  total  observed  barometric  pressure  of  740  mm.  of 
mercury,  the  actual  pressure  of  the  gas  in  the  burette  at  the 
different  temperatures  is  therefore, 

for  20°  C.,  740-17.4  =  722.6; 
for  21°  C.,  740-18.5-721.5; 
for  22°  C.,  740-19.7  =  720.3; 

and  the  corrected  volume  of  the  81  c.c.  at  21°  C.  allowing  for  this 
change  is  less  by of81=0.12c.c.  and  the  corrected  volume  of 

2.3 

the  81  c.c.  observed  at  22°  C.  is  less  by  of  81  =  approximately 

/20.3 

0.26  c.c.  This  error  adds  to  the  error  introduced  by  the  tempera- 
ture changes. 

Combining  the  two  corrections,  the  true  reading  and  percentages 
are  as  follows: 


Observed 

Observed 

Corrected 

to  20°  C. 

Reading. 

Per  Cent. 

True  Reading. 

True   Per  Cent. 

Initial  reading  
CO2  
O2  

0.00 
10.00 
19.00 

10.00 

9.00 

10.00 
19.40 

10.00 

9  40 

CO. 

19  00 

0  00 

19  81 

41 

N2  

81  00 

80  19 

100.00 

100.00 

The  above  corrections  are  obtained  as  follows: 

For  oxygen,  correcting  from  21°  to  20°  C.  =  100-19  =  81  c.c. 


ANALYSIS  OF  FLUE  OASES  149 

293     721  5 

<MU^799"fi  =  ^'^'     The   correct   oxygen   reading   is   there- 

fore 100  -  80.60  =  19.40. 

For  carbon  monoxide,  correcting  from  22°  to  20°  C.,  100-19 

293     720  3 
=  81   c.c.  81XX  =  80.19.     The  correct  carbon  monoxide 


reading  is  therefore  100-80.19  =  19.81. 

With  an  initial  temperature  of  20°  C.,  a  change  of  1°  during 
the  determination  of  any  constituent  introduces  an  error  of  about 
0.4  per  cent.  If  the  temperature  has  increased  the  observed  result 
is  too  low.  If  the  temperature  has  decreased  the  observed  result 
is  too  high.  For  higher  temperatures  the  effect  of  aqueous  tension 
is  appreciably  larger.  For  30°  C.  (89°  F.)  the  error  for  1°  change 
of  temperature  being  approximately  0.06  per  cent  more  than  at 
20°  C. 

The  magnitude  of  these  errors  certainly  shows  the  impossibility 
of  securing  accurate  results  with  unjacketed  burettes  and  shows 
the  possibility  of  serious  errors  even  where  jacketed  burettes  are 
used,  if  the  apparatus  is  exposed  to  draughts  or  rapid  temperature 
changes.  The  use  of  a  thermometer  in  the  water  jacket  and  the 
taking  of  temperature  observations  before  and  after  the  absorp- 
tion serve  as  a  check  on  this  error  and  allow  for  corrections  if 
temperature  changes  are  noted. 


ALTERATION  OF  SAMPLES  ON  STANDING  AND  EFFECTS 
UPON  THE  ORSAT  RESULTS 

The  foregoing  discussion  of  the  Orsat  analysis  and  results  is 
based  on  the  supposition  that  the  samples  are  drawn  directly  into 
the  Orsat  apparatus  and  analyzed  at  once.  When  samples  are 
collected  in  sample  tubes  or  bottles,  or  in  metal  tanks,  the  possible 
and  probable  alteration  of  the  samples  and  the  effect  upon  the 
Orsat  determination  should  be  considered. 

The  changes  to  which  a  stored  sample  are  liable  are,  (1) 
leakage,  (2)  chemical  changes,  (3)  absorption  of  the  gas  in  the  water 
over  which  it  is  collected  or  over  which  it  is  allowed  to  stand. 

(1)  Leakage.  The  danger  from  alteration  of  a  stored  sample 
from  leakage  should  not  be  overlooked.  Samples  stored  in  rubber 
containers  or  in  containers  with  rubber  connections  of  any  length 


150  COAL' 

are  practically  sure  to  alter  if  kept  for  any  considerable  time, 
and  sample  tubes  closed  by  stop-cocks  even  if  well  lubricated  and 
well  tied  are  liable  to  possible  leakage.  A  slight  leak  in  a  rubber 
connection  or  around  a  stop-cock,  if  the  sample  is  analyzed 
promptly,  may  not  have  any  measurable  effect  upon  the  sample 
but  if  the  sample  is  stored  and  the  leakage  allowed  to  continue 
during  twenty-four  or  forty-eight  hours  the  sample  may  be  so 
changed  in  composition  as  to  render  any  results  obtained  upon 
it  entirely  worthless.  Every  rise  or  fall  in  the  temperature  of 
the  gas  from  that  at  which  it  was  collected  subjects  it  to  an  in- 
creased or  diminished  pressure  and  hence  any  slight  leaks  are 
likely  to  be  continually  acting. 

If  samples  must  be  collected  and  kept  before  being  analyzed 
the  author  prefers  to  so  take  them  that  they  will  be  under  con- 
siderable pressure  when  sealed  and  any  leakage  be  continually 
outward  rather  than  alternately  inward  and  outward.  Also  if 
collected  and  kept  over  water  the  exposure  to  water  while  collect- 
ing should  be  reduced  to  a  minimum  and  the  amount  of  water 
allowed  to  remain  in  contact  with  the  sample  should  be  relatively 
small  in  comparison  to  the  volume  of  the  sample.  (For  example 
preferably  not  over  one  volume  of  water  to  10  volumes  of  gas.) 

Leakage  of  sample  outward  may  merely  change  the  volume  of 
the  sample  without  altering  its  composition.  However,  as  carbon 
dioxide  diffuses  through  small  orifices  less  readily  than  the  lighter 
gases  (oxygen,  nitrogen  and  carbon  monoxide),  a  considerable 
leakage  of  gas  especially  if  through  rubber  may  result  in  the 
residual  gas  being  higher  in  carbon  dioxide  than  the  original  sample. 
Leakage  inward  is  certain  to  raise  the  oxygen  content  since 
the  oxygen  percentage  of  the  air  surrounding  a  sample  is  certain 
to  be  much  higher  than  the  oxygen  content  of  the  flue-gas  sample. 
The  effects  of  leakage  and  consequent  alteration  of  the  composi- 
tion of  the  sample  upon  the  value  of  the  Orsat  determination  are 
discussed  in  detail  later. 

(2)  The  chemical  alteration  of  the  sample.  The  chief  sources 
of  error  from  chemical  changes  are  the  absorption  of  oxygen  by 
reducing  reagents  in  the  water  over  which  the  sample  is  collected 
or  stored,  and  the  absorption  of  carbon  dioxide  as  carbonate  by 
salts  of  calcium  which  may  be  in  the  water,  or  in  some  cases  the 
enrichment  of  the  gas  in  carbon  dioxide  by  its  liberation  from 
bi-carbonate  salts  in  the  water.  The  usual  reducing  agents  are  the 


ANALYSIS  OF  FLUE  GASES 


151 


ferrous  salts  of  iron  which  readily  use  up  oxygen,  and  water  which 
carries  iron  in  solution  should  not  be  used  in  filling  the  tanks  or 
tubes  in  which  gas  samples  are  to  be  collected.  Rain-water,  well 
water  or  hydrant  water  which  has  been  exposed  to  the  air  for  some 
time  before  using  is  to  be  preferred  to  water  taken  directly  from 
the  pump  or  water  main.  The  water  should,  however,  not  be 
too  thoroughly  aerated,  as  if  saturated  with  air  it  will  give  up 
oxygen  to  flue-gas  samples  kept  over  it.  To  avoid  as  much  as 
possible  errors  from  chemical  changes,  the  exposure  of  the  sample 
to  water  should  be  reduced  to  a  minimum  and  only  a  small  amount 
of  water  be  allowed  to  remain  in  contact  with  the  sample. 


ALTERATION  OF  SAMPLES  BY  ABSORPTION  IN  THE  WATER 
OVER  WHICH  THEY  ARE  COLLECTED  OR  STORED 

Samples  collected  over  water  are  certain  to  suffer  alteration 
from  this  cause  and  the  extent  of  such  alteration  and  the  effect 
upon  the  Orsat  determination  should  be  well  understood  by  every- 
one who  has  to  do  with  gas  sampling. 

The  following  values  for  solubilities  are  taken  from  Landolt 
and  Bernstein's  tables,  the  solubilities  being  given  in  volumes  of 
gas  absorbed  by  one  volume  of  water  at  the  temperatures  given 
and  with  the  gas  at  a  pressure  of  760  mm.  of  mercury. 


0°  C.  (32°  F.). 

15°  C.  (59°  F.). 

30°  C.  (86°  F.). 

O2 

0  0489 

0  03415 

0.02608 

N2  

0  .  02388 

0.01786 

0.01380 

CO 

0  03537 

0  02543 

0.01998 

CO2  

1.713 

1.019 

0.665 

The  solubilities  of  these  gases  for  the  same  temperature 
varies  directly  as  the  pressure  of  the  gas  and  for  a  mixture  of  gases 
the  solubility  of  each  gas  is  proportional  to  the  partial  pressure  of 
each  gas  independent  of  the  other  gases  present.  The  partial 
pressure  exerted  by  each  gas  in  a  gas  mixture  is  proportional  to 
the  percentage  of  each  gas.  For  example  in  a  mixture  of  20  per 
cent  oxygen  and  80  per  cent  nitrogen  under  atmospheric  pressure 


152  COAL 

the  partial  pressure  of  the  oxygen  is  0.20  of  an  atmosphere  and 
the  partial  pressure  of  the  nitrogen  is  0.80  of  an  atmosphere. 

The  solubility  of  a  mixture  of  gases  (flue  gas)  in  water  should  be 
considered  under  several  particular  conditions : 

(1)  An  unlimited  supply  of  gas  and  a  limited  supply  of  water. 
With  an  unlimited  supply  of  gas  and  a  limited  supply  of  water 
the  volumes  of  gas  which  can  be  absorbed  by  the  water  at  any 
given  temperature  and  pressure  may  be  calculated  directly  from 
the  solubility  values  previously  given. 

(2)  A  limited  supply  of  gas  and  an  unlimited  supply  of  water. 
With  a  limited  supply  of  gas  and  an  unlimited  supply  of  water 
the  gas  will  be  entirely  dissolved  in  the  water. 

(3)  A  limited  supply  of  gas  and  a  limited  supply  of  water.     With 
a  limited  supply  of  gas  and  a  limited  supply  of  water  the  gas  will 
dissolve  in  water  until  a  condition  of  equilibrium  is  attained. 
This  condition  of  a  limited  supply  of  gas  and  a  limited  supply 
of  water  is  the  one  that  exists  where  gases  are  stored  in  sampling 
tubes  or  containers  over  water  and  the  possible  alteration  of  such 
samples  should  be  well  understood.     This  may  perhaps  best  be 
shown  by  an  example.     For  illustration,  what  is  the  solubility 
and  the  resultant  volume  and  composition  of  one  liter  of  gas 
stored  over  one  liter  of  pure  distilled  water  at  a  temperature  of 
15°  C.  (59°  F.),  at  an  atmospheric  pressure  of  742.7  mm.  of  mer- 
cury, the  composition  of  the  original  gas  being, 

CO2  10.0  per  cent 
O2  9.0 

CO  0.5 

N2  ?80.5 


100.0 

The  pressure  of  aqueous  vapor  at  15°  C.  =  12.7  mm.  of  mercury 
or  the  total  pressure  of  the  gas  present  =  742. 7  — 12.7  =  730  mm. 
of  mercury.  From  the  values  for  solubilities  given  for  760  mm. 
pressure  of  gas  and  15°  C.  the  solubilities  of  CO2,  62,  CO,  and 
N2  in  1000  c.c.  of  water  for  730  mm.  are  found  to  be, 

C02  =  978.8    c.c. 

O2=  32.79   ll 

C0=   24.42   " 

N2=   17.17   " 


ANALYSIS  OF  FLUE  GASES  153 

Since  the  partial  pressure  of  each  constituent  of  a  mixture  is 
proportional  to  the  percentage  of  each  constituent  present,  the 
solubilities  of  the  different  gases  in  1000  c.c.  of  water  at  15°  C. 
(assuming  an  unlimited  supply  of  gas)  are  as  follows: 

CO2  =  978.8  X^  =97. 88  c.c. 

1UO 

02=   32.79X^  ;   =   2.94  " 

1UU 

00=24.42x14=0.12." 

N2=   1 


For  1000  c.c.  of  the  original  gas  the  volumes  of  the  constituents 
arc  as  follows: 

10      per  cent  C02  =  100  c.c. 

9            "       O2    -  90   " 

0.5        "       CO  =  5   " 

80.5        "       N2    -  805   " 


100.0  1000   ( 

Comparison  of  the  amount  of  each  gas  in  1000  c.c.  of  the 
mixture  with  the  solubility  in  1000  c.c.  of  water  based  on  the 
supposition  of  an  unlimited  supply  of  gas  shows  at  a  glance  that 
the  solubility  of  oxygen,  carbon  monoxide  and  nitrogen  from  the 
limited  supply  of  gas  (1000  c.c.)  is  not  very  far  from  the  amount 
taken  up  from  an  unlimited  supply,  since  the  amount  of  each 
dissolved  is  small  compared  to  the  amount  of  each  present  in 
1000  c.c.  of  the  gas. 

With  an  unlimited  supply  of  gas  the  solubility  of  carbon 
dioxide  is  97.88  c.c.  Since  the  total  c.c.  of  carbon  dioxide  in  one 
liter  of  the  gas  is  only  100  c.c.  if  this  amount  were  absorbed,  only 
2.14  c.c.  of  carbon  dioxide  would  be  present  in  the  residual  gas. 
The  volume  of  the  residual  gas,  allowing  for  this  absorption  and 
allowing  for  the  absorption  of  oxygen,  carbon  monoxide  and 
nitrogen  is  885  c.c.  or  the  2.14  c.c.  of  carbon  dioxide  =  2.4  per  cent 


154  COAL 

of  the  residual  gas.  The  solubility  of  carbon  dioxide  in  1000  c.c. 
of  water  with  this  per  cent  present  in  the  gas  over  the  water  is 
978.8X0.024  =  approximately  2.3  c.c.  and  the  actual  condition  of 
equilibrium  for  solubility  of  the  carbon  dioxide  in  the  1000  c.c.  of 
water  is  evidently  somewhere  between  these  two  extremes  of 
solubility,  2.3  c.c.  and  97.88  c.c.  or  something  over  50  c.c. 

As  a  preliminary  approximation,  assume  the  solubility  of 
carbon  dioxide  from  the  limited  volume  of  gas  (1000  c.c.)  to  be 
51  c.c.;  oxygen  3  c.c.;  and  carbon  monoxide  0.12  cc..  and  for 
nitrogen  14  c.c.,  then  the  amounts  and  percentages  of  gas  remain- 
ing are  as  follows: 

CO2  =  100  -     51  =•  49        c.c.  =   5 . 26  per  cent 
O2    =  90-     3   =  87         "  =  9.33       " 
CO  =      5-0.12=     4.88   "  =  0.52 
N2    =805-     14  =  791.        "  =84.89       " 


Total          931.88   '       100.00       ll 

Multiplying  the  solubility  of  each  gas  at  730  mm.  pressure 
and  at  15°  C.  by  the  percentage  of  gas  remaining,  the  amounts 
of  gas  dissolved  in  1000  c.c.  for  these  percentages  are  as  follows: 

CO2  =  978.8  XO. 0526  =  51. 48    c.c. 
O2      =   32.79X0.093   ==  3.04     " 
CO  ==   24.42X0.0052=  0.127   " 
N2    =   17.17X0.849   =14.58     " 

From  which  it  is  seen  that  the  first  approximation  for  solubility 
does  not  give  actual  equilibrium,  but  a  second  approximation 
using  values  based  on  the  ones  already  obtained  will  give  practical 
equilibrium. 

These  values  are  about  as  follows : 

CO2  absorbed  =  51. 25  c.c. 
02  "        =  3.05   " 

CO  =  0.13   " 

N2          "        =14.6     " 


ANALYSIS  OF  FLUE   GASES  155 

Using  these  values  the  volumes,  percentages  and  equilibrium 
conditions  are  as  follows: 


-         P«  Cent. 

CO2  =  100  -51.25=  48.75=  5.24=51  .28  c.c. 

02=   90-  3.05=   86.95=  9.34=   3.06    " 

CO=     5-0.13=     4.87=  0.52=0.13    " 

N2  =  805-14.6   =790.4   =  84.90  =  14.6      " 


Total  930.97     100.00 

The  values  obtained  serve  to  show  the  possible  changes  that 
gas  stored  over  water  may  undergo.  The  actual  solubilities 
under  working  conditions  will  differ  from  these  values  on  account 
of  the  fact  that  ordinary  water  contains  dissolved  in  it  some 
carbon  dioxide,  oxygen  and  nitrogen,  hence  the  solubilities  under 
ordinary  conditions  will  not  be  as  high  as  the  calculated. 

Chemical  changes  may  also  enter  in  to  alter  the  composition 
of  the  final  sample  so  that  any  calculated  solubility  change  can- 
not be  depended  upon  for  great  accuracy. 

The  values  obtained  in  the  foregoing  illustration  serve,  how- 
ever, to  emphasize  and  make  clear  the  following  facts : 

That  the  alteration  of  the  sample  in  carbon  dioxide  may  be 
very  great  and  that  the  composition  of  the  remaining  sample  is 
as  a  result  higher  in  both  oxygen  and  nitrogen. 

Effect  of  the  solution  of  CO2  upon  other  determinations. 
The  excess-air  ratio  as  determined  by  the  ratio  between  oxygen  and 
nitrogen  is  not  however  affected  by  the  solubility  of  carbon  dioxide 
and  in  so  far  as  carbon  dioxide  is  concerned  the  excess  air  may  be 
determined  almost  as  accurately  on  a  stored  sample  as  on  one 
freshly  taken,  provided  of  course  that  chemical  changes  have  not 
used  up  oxygen. 

In  the  illustration  given  above,  the  excess  air  in  the  original 
sample  containing  10  per  cent  of  carbon  dioxide  calculated  from 
the  oxygen-nitrogen  ratio,  is  73.9  per  cent.  The  excess  air  in  the 
sample  after  it  has  reached  equilibrium  over  the  1000  c.c.  of  water 
is  71.8  per  cent  or  a  change  of  only  2  per  cent  in  the  figured  excess 
air  with  a  change  of  nearly  5  per  cent  in  carbon  dioxide  (nearly 
one-half  of  the  amount  originally  present)  and  a  change  of  over  4 
per  cent  in  nitrogen. 

The  calculation  of  heat  loss  due  to  formation  of  carbon  mon- 
oxide rather  than  carbon  dioxide  is  made  inaccurate  by  any 


156  COAL 

absorption  of  carbon  dioxide.  In  the  original  sample  the  amount 
of  carbon  burned  to  carbon  monoxide  is  yj-g-  of  the  total  carbon 
in  the  coal,  while  in  the  sample  which  has  reached  equilibrium 
over  the  1000  c.c.  of  water,  the  carbon  burned  to  carbon  monoxide 
is  -j5726  of  the  total  carbon  present,  or  a  ratio  almost  twice  as  large 
as  the  true  ratio  r~(hr>  so  that  with  large  amounts  of  carbon  mon- 
oxide present  in  the  gas  the  absorption  of  carbon  dioxide  in  the 
water,  before  the  determination  of  the  Orsat  analysis,  makes  the 
heat  balance  inaccurate  in  so  far  as  the  heat  loss  due  to  carbon 
monoxide  is  concerned,  but  for  the  more  important  item  of  excess 
air  the  absorption  of  carbon  dioxide  is  without  effect. 


EFFECT  OF  A  WATER  SEAL  UPON  COMPOSITION  OF 
SAMPLES 

Where  samples  are  stored  in  bell  jars  or  inverted  cylinders 
and  protected  from  the  atmosphere  by  a  water  seal  the  action  of 
this  water  seal  should  be  noted.  The  surface  of  the  water  in  con- 
tact with  the  gas  continually  tends  to  reach  a  condition  of  equilib- 
rium with  respect  to  the  gas  above  it.  Likewise  the  surface  of 
the  water  seal  which  is  exposed  to  the  air  is  continually  tending 
to  reach  a  condition  of  equilibrium  with  respect  to  the  air  above 
it.  Since  the  composition  of  the  stored  gas  and  the  composition 
of  the  air  on  the  outside  are  radically  different,  equilibrium  con- 
ditions on  the  two  sides  are  different  and  the  result  is  a  continual 
absorption  of  carbon  dioxide  from  the  sample  into  the  water  which 
gradually  diffuses  through  the  water  seal  and  escapes  into  the  open 
air  on  the  other  side.  Likewise  there  is  in  the  opposite  direction  a 
continual  absorption  of  oxygen  from  the  air  into  the  water  and  dif- 
fusion of  this  oxygen  through  the  water  seal  into  the  stored  gas. 
The  final  effect,  if  the  sample  is  stored  long  enough,  will  be  that 
the  composition  of  the  sample  will  approximate  that  of  the  outside 
air,  the  excess  carbon  dioxide  and  carbon  monoxide  gradually 
diffusing  and  escaping  and  the  oxygen  content  of  the  sample  con- 
tinually increasing  from  diffusion  inward.  On  account  of  this 
diffusive  action  the  author  prefers  in  storing  samples  over  water 
that  there  be  no  actual  contact  of  the  water  seal  with  the  outside 
air. 

Details  of  the  determination  of  hydrogen  and  hydro-carbons 


ANALYSIS  OF  FLUE  GASES  157 

in  the  flue  gases  and  are  given  in  special  texts  upon  gas  analysis- 
The  determination  of  carbon  monoxide  as  made  in  the  Orsat 
apparatus  is  satisfactory  only  when  small  amounts  of  carbon 
monoxide  are  present  in  the  gas,  as  is  the  case  in  a  boiler  flue 
gas.  In  the  analysis  of  a  gas  high  in  carbon  monoxide,  as  gas 
from  an  iron  blast  furnace  or  gas  from  a  gas  producer,  the 
method  and  apparatus  used  should  be  such  as  to  secure  rapid 
and  complete  absorption  of  the  large  amount  of  carbon  monoxide 
present.  For  the  description  of  suitable  methods  and  apparatus 
special  texts  on  gas  analysis  should  be  consulted. 


CHAPTER  X 

ANALYTICAL  TABLES 

COMPARATIVE  COMPOSITION  OF  DIFFERENT  FUELS 


Fuel. 

Moisture,  Per  Cent. 

Remarks. 

Wood 

30  to  60 

Green  wood 

Peat  

50  to  90 

As  dug. 

Lignite 

30  to  45 

As  minod 

Bituminous  coal 
Semi-bituminous  coal.  .  .  .  .*  

2  to  25 
1  to    5 

As  mined. 
As  mined 

Anthracite  coal. 

1  to    3 

As  mined 

COMPOSITION  AND  HEATING  VALUE  OF  AIR-DRIED  MATERIALS 


Wood. 

Peat.s 
Florida 
No.  1. 

Lig- 
rute,1 
North 
Dakota 
No.  2. 

Bituminous  Coal. 

Semi- 
bitu- 
minous 
Coal.i 

Anthra- 
cite 
Coal.i 

Illinois,1 
No.  6. 

Ohio, 
Hock- 
ing,4 

Penn. 
No.  5. 

Pitts- 
burgh.2 

W.  Va. 

No.  7, 
New 
River. 

Penn. 
No.  3. 

Proximate: 
Moisture  
Vol.  matter  

20.0 

21.00 
51.72 
22.11 
5.17 

16.70 

37.10 
39.49 
6.71 

5.13 
32.68 
47.46 
14.73 

3.00 
39.00 
50.50 
7.50 

1.00 
35.00 

57.85 
6.15 

0.76 
20.54 
73.61 
5.09 

2.08 

7.27 
74.32 
16.33 

Fixed  carbon  

Ash  

Ultimate: 
Carbon  

40.0 

7.2 
.8 
50.7 

100.00 

46.57 
6.51 
2.33 
38.97 
5.17 
.45 

100.00 

55.16 
5.61 
.91 
30.98 
.63 
6.71 

100.00 

60.51 
4.88 
1.23 
14.20 
4.45 
14.73 

100.00 

70.70 
5.20 
1.30 
11.95 
3.35 
7.50 

100.00 

78.75 
5.14 
1.55 
7.56 
.90 
6.10 

100.00 

82.41 
4.38 
1.05 

5.87 
1.20 
5.09 

100.00 

75.21 

2.81 
.80 
4.08 
.77 
16.33 

Hydrogen  
Nitrogen  

Oxygen  

Sulphur  

Ash  

1.3 

Determined    calo- 
rific value  = 
Calculated      calo- 
rific value  -T- 

100.0 
4200 

100.00 

4515 
4338 

100.00 

5273 
5071 

100.00 

6199 
6059 

100.00 

7155 
7100 

100.00 

7865 
.7845 

100.00 

8254 
7942 

100.00 

6929 

6886 

1  U.S.G.S.  Professional  Paper  No.  48. 

2  U.S.G.S.  Bulletin  No.  290. 


s  U.S.G.S.  Bulletin  No.  332. 

*  Ohio  Geol.  Survey,  Bulletin  No. 

158 


ANALYTICAL  TABLES 


159 


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161 


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§COC5t--OCO'OOOOOiOOt^< 


"*|cO'-i^cO'-H 

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<o  co  10  o  -*  r-c  -^  oo  *•  10  os 

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coooiococococo^cocooco 

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co  co     •  t^-  co  co     -co 

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cs  ic  co  os  os  I-H 

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Marion  Co  
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6    '  6        '.  o  *S  6 
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rH   CM   CO   *#   Ifi 

CO 

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««» 

ANALYTICAL  TABLES 


163 


•,,uo,,nv 

rH  <M  CO  CM  CM  CO 

« 

rHrHCOrHrHfOCOCOCO 

rH  CO  CO 

rH   rH   CO  CO   CO   CO 

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CM   CD   00  CO  CO   O3 
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3 

co 

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10    O    05    0    rH    C5 
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10    LO    LO 

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CD  LO  CO  CO  CD  CD 

pauiuuaiaQ 

O5  O5  O  iO  LO  iO 

CO  CO  b-  b-  CO  CO 
CO  CO  CO  b-  b-  b- 

CD 

e 

rH    IO    IO    rH    b-    O    OO    Tfl    O 

OOiOiOrHCOcDOOb- 
COCDOO5C500C5OC5 
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LO    rH    CD 

rH    Tt<    b-    05    GO    O 

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10  10  iO  l>  b-'  CM 
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10 

b- 

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05  00  O 
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b-CMCMCOCOCOOOCOCO 

t^  CD  CO 

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ANALYTICAL  TABLES 


167 


INDEX 


Accuracy  of  chemical  work,  51,  52. 

Acid, 

cuprous  chloride  solution,  138; 
nitric,  correction  for  formation  of, 
95,  99;  pyrogallic,  138;  standard, 
89;  sulphuric,  correction  for  forma- 
tion of,  100;  sulphuric,  use  of,  in 
desiccators,  81. 

Air, 

composition  of,  16;  drier  for  coarse 
samples,  71;  drying  of  samples, 
70;  excess,  16,  142;  excess,  calcu- 
lation of,  16;  specific  heat  of,  24. 

Alteration  of  samples,  76,  149,  151. 

Alumina,  effect  on  fusibility  of  ash,  5. 

Amperes,  required  to  ignite  wire  fuse, 
100. 

Analysis  of  coal,  79-90. 

determination  of  ash,  81;  of  car- 
bon, 86;  of  fixed  carbon,  83;  of 
hydrogen,  86;  of  moisture,  79;  of 
nitrogen,  88;  of  oxygen,  90;  of 
phosphorus,  89;  of  proximate  com- 
position, 43-45;  of  sulphur,  83; 
of  ultimate  composition,  85;  of 
volatile  matter,  82. 

Analysis  of  gas,  132. 

for  carbon  dioxide,  137;  tor  carbon 
monoxide,  137;  for  nitrogen,  132; 
for  oxygen,  137. 

Analytical  records, 
forms  of,  119;   meaning  of,  119. 

Analytical  tables,  158-168. 

Anthracite  coal,  analysis  of,  158. 


Apparatus, 

for  analyzing  gas,  134;  for  sampling 
gas,  133;  for  sampling  laboratory, 
76;  for  washing  coal,  123;  Orsat, 
134. 

Aqueous    tension,    effect    of   on   re- 
sults of  gas  analysis,  148. 

Asbestos  disc,  use  of  in  calorimetric 
work,  96. 

As"h  in  coal, 

amount  of,  6;  clinkering  of,  8; 
composition  of,  4;  corrected,  3; 
determination  of,  81;  distribution 
of,  6;  effect  of  on  commercial  value, 
128;  fusibility  of,  4;  meaning  of 
term,  3;  removal  of,  by  washing, 
122;  specific  heat  of,  24. 

Available  heating  power  of  coal,  13. 
calculation  of,  25;    effect  of  mois- 
ture on,  37;  variation  of,  36. 

B 

Ball  mill  grinding,  72;  advantage  of, 

75,  76. 

Benzoic  acid,  calorific  value  of,  106. 
Bituminous  coal,  composition  of,  158. 
Boiler  flues,  sampling  gas  from,  133. 
Boiler  Tests, 

heat  balance  of,   28,   32,  33,   34; 

need  of,  14. 
British  thermal  unit, 

definition    of,    9;     relation   of,    to 

calorie,  10. 
British  thermal  value,  relation  of,  to 

calorific  value,  9. 

169 


170 


INDEX 


Bucking  board  grinding,  76. 
losses  of  moisture  during,  75. 

Bureau  of  Mines, 

bulletins,  No.  5,  125,  159;  No.  41, 
Purchase  of  Coal,  131;  Technical 
Paper,  No.  1,  sampling,  63;  sam- 
pling outfit  used  by,  63. 

Bureau  of  Standards, 

calibration  of  thermometer  by, 
110;  circular  No.  8  of,  on  thermo- 
meters, 111;  standards  furnished 

[    by,  106. 


Calcium  chloride, 

use  in  desiccators,  81;  solution  of, 
for  washing  coal,  124. 

Calculation  of, 

calorific  determination,  94;  calori- 
fic value,  10;  heat  balance,  13-23; 
heating  power  of  Ohio  No.  6  coal, 
25-32;  heating  value  of  coal  from 
proximate  analysis,  39;  ultimate 
analysis,  54. 

Calibration  of  thermometers,  107. 

Calorie, 

definition  of,  9;  relation  to  British 
thermal  unit,  10. 

Calorific  value, 

calculating  the,  10,  39,  41;  deter- 
mining the,  91-118;  of  benzoic 
acid,  106;  of  cane  sugar,  106;  of 
carbon,  10,  11;  of  coal,  9;  of  coals, 
53,  158-168;  of  naphthalene,  106; 
relation  of,  to  British  thermal 
value,  9;  special  notes  on  the 
determining  of,  96. 

Calorimeter, 

kinds  of,  91 ;  leakage  around  lid  of, 
97;  method  of  operating  a,  91-92; 
use  of  cover  for,  117;  valve, 
preventing  leakage  of,  96;  wash- 
ings, sulphur  in,  85;  water  equiv- 
alent of,  105. 

Calorimeter  determination, 

corrections  to,  95;  method  of  cal- 
culation, 93-94. 


Cane  sugar, 

calculation  of  calorific  value  of,  12; 
calorific  value  of,  106. 

Cans,  for  coal  samples,  61,  63. 

Carbon, 

calorific  value  of,  10,  11;  deter- 
mination of,  86;  fixed,  83. 

Carbon  dioxide, 

absorption  by  potassium  hydroxide 
solution,  139;  absorption  in  water, 
151;  determination  of,  in  flue  gas, 
137;  effect  of  solution  of,  upon 
excess  air  calculation,  155;  specific 
heat  of,  24. 

Carbon  monoxide, 

absorption  by  cuprous^1  chloride 
solution,  140;  calculation  of  car- 
bon burned  to,  19;  determination 
of,  in  flue  gas,  137,  157;  heat  loss 
due  to,  19;  solubility  in  water, 
151;  specific  heat  of,  24. 

Car  sampling,  63,  70. 

Cathetometer,  use  of,  92,  108. 

Centigrade      degree,       relation      to 
Fahrenheit  degree,  9. 

Chemical  determinations,  summary  of, 
119. 

Chute,  sampling,  64-65. 

Clinker  in  coal, 

formation  of,  5,  6;  influence  of 
sulphur  on,  8. 

Coal, 

analysis  of,  79-90;  anthracite, 
composition  of,  158;  ash  of,  3-6,  8, 
45;  bituminous,  composition  of, 
158;  calorific  value  of,  9,  10,  46; 
clay  in,  4;  combined  water  in,  48; 
combustible  matter  in,  44,  49; 
commercial  value  of,  37,  126; 
composition  of,  45-53,  158-168; 
dry,  120;  drying  of,  70;  fixed  car- 
bon in»  45;  heating  value  of,  9, 
10,  39,  53,  158-168;  hydrogen  in, 
available,  48,  total,  48;  improve- 
ment by  washing,  122-125;  mois- 
ture in,  2,  43,  48,  80,  81;  nature  of, 
VII;  nitrogen  in,  47,  88;  origin  of, 
VII;  oxygen  in,  11,  48,  51,  52,  90; 


INDEX 


171 


phosphorus  in,  89;  purchase  of, 
126-131;  pyrite  in,  6,  66,  122; 
residual,  38,  51;  slate  in,  4,  66, 
122;  sulphur  in,  6,  7,  46,  49,  66, 
83,  122;  unburned,  20;  heat  loss 
due  to,  20;  calculation  of  loss  due 
to,  20;  variation  in,  VII;  volatile 
matter  in,  44,  49,  82;  weathering 
of,  VIII. 

Coals  of  United  States,  composition 
of,  159-168. 

Code,  heat  balance,  34. 

Combustion, 

incomplete,  19;  products  of,  15; 
reactions  of  complete,  141 ;  specific 
heats  of  products  of,  23. 

Commercial  value  of  coal,  37. 

estimation  of,  126;  factors  affect- 
ing, 126. 

Cover,  use  of,  on  calorimeter,  117. 

Crusher  for  reduction  of  samples,  76. 

Crushing  rolls,  77. 

Cuprous  chloride  solution, 

absorbing  power  of,  140;  prepara- 
tion of,  138. 

Current,  electric, 

for  igniting  iron  wire,  100;  leakage 
of,  in  calorimeter  determination, 
104. 

D 

Damour,  specific  heats  according  to, 

23-24. 

Density  of  water,  98. 
Desiccators,  use  of  sulphuric  acid  in, 

81. 

Dewar  flask,  109. 
Dew   point,    effect   on    calorimetric 

work,  98. 

Drier  for  coarse  samples,  71. 
Dry  coal,  120. 
X)ulong's  formula,  10. 

modification  of,  12. 

E 

Electric  current, 

heat  developed  by,  102  ;  use  of 
for  igniting  wire  fuse,  100. 


Equipment, 

for  laboratory  washing  of  coal,  123; 
for  reduction  of  samples  of  coal, 
76;  for  sampling  coal  in  the  mine, 
61. 

Errors, 

in  calorific  determination,  96-117; 
in  chemical  determinations,  52,  57; 
in  gas  analysis,  137-149;  in  sam- 
pling coal,  57,  60,  66;  in  sampling 
gas,  133;  in  specific  heats  of  gases, 
24;  in  thermometers,  107;  in 
water  equivalent  of  calorimeter, 
105. 

Eschka  method  for  sulphur,  83. 

Excess  air,  16. 

calculation  of,  16-18;  effect  of 
solution  of  carbon  dioxide  upon 
calculation  of,  155. 


Fahrenheit  degree,  relation  to  Centi- 
grade degree,  9. 

Fixed  carbon, 

determination  of,  83;  heating 
value  of,  45;  in  coal,  45. 

Flasks,  use  of,  in  calorimetric  work, 
97. 

Flue  gases, 

analysis  of,  132-157;  composi- 
tion of,  132;  sampling  of,  132. 

Formula, 

for  calculating  excess  air,  16;  for 
calculating  heating  value,  10,  12; 
for  calculating  unburned  coal,  20. 

Fuels,   comparative   composition  of, 
158. 


G 


Gas, 


flue  gas,  analysis  of,  132-157;  ap- 
paratus for  analyzing,  134;  com- 
position of,  132;  sampling  of,  132. 
reactions,  calculation  of,  in  molec- 
ular volumes,  141;  samples,  ab- 
sorption in  water,  151,  152;  alter- 
ation of,  149-150;  changes  in, 


172 


INDEX 


152;    keeping  of,  over  water,  151; 

leakage  of,   149;    taking  of,   132; 

tubes  for,  133. 
Gases, 

solubility  of,  in  water,  151;  specific 

heats  of,  24. 
Grinding  of  samples, 

in  ball  mill,  72;  on  bucking  board, 

76. 


"  H," 

calculation  of,  39;  definition  of, 
39;  variation  of,  for  different  coals, 
47. 

Heat, 

developed  by  electric  current,  102; 
developed  in  calorimeter  by  leak- 
age of  current,  103,  104;  latent, 
of  water  vapor,  15;  mechanical 
equivalent  of,  116. 

Heat  balance, 

calculation  of  boiler  heat  balance, 
13-32;  calculation  of,  using  printed 
forms,  28-29;  calculation  of,  using 
thermal  capacity  tables,  31;  of 
American  Society  of  Mechanical 
Engineers,  34;  on  coal  as  fired,  33, 
as  burned,  33;  on  combustible 
fired,  33,  burned  33;  on  dry  coal 
fired,  33,  burned,  33;  separation 
of  losses  in,  34-35. 

Heating  value  of  coal, 

available,  13,  variation  of,  36; 
British  thermal  value  of,  9;  cal- 
culation of,  from  ultimate  analysis, 
10;  from  proximate  analysis  and 
from  "  H,"  39;  calorific  value  of, 
9;  determination  of,  91;  total,  9. 

Heat  losses  during  combustion,  14-23; 
from  formation  of  carbon  mon- 
oxide, 19;  from  incomplete  com- 
bustion, 19,  21;  from  radiation, 
21;  in  excess  air,  14,  26;  in  latent 
heat  of  products  of  combustion, 
14-15;  in  sensible  heat  of  products 
of  combustion,  13-21;  unaccounted 
for,  21. 


Heat  producing  constituents  in  coal, 
10. 

Hydrocarbons,  21. 

effect  of,  on  determination  of 
nitrogen  in  flue  gas,  146. 

Hydrogen, 

available,  48;  determination  of, 
86;  effect  of,  on  observed  calorific 
value,  116;  effect  of  unburned  on 
determination  of  nitrogen  in  flue 
gas,  146;  heating  value  of,  10,  21; 
in  coal,  117;  in  naphthalene,  116; 
in  petroleum,  117;  total,  48;  un- 
burned in  flue  gas,  21. 


Incomplete  combustion,  19. 

Iron  in  coal  ash,  3,  8. 

Iron  wire, 

correction  for,  95;  current  and 
voltage  for  igniting,  100;  ignition 
of,  100. 

K 

Kjeldahl  method  for  nitrogen,  89. 


Latent  heat  of  evaporation  of  water, 
15. 

Leakage, 

around  lid  of  calorimeter,  97;  of 
electric  current  during  a  calor- 
imeter determination,  102,  104; 
of  valve  of  calorimeter,  96. 

Lewis    and    Randall,    specific    heats 
according  to,  24. 

Lignite, 

moisture  in,  2;  North  Dakota,  46, 
53,  158. 

Logarithms,  calculation  of  heat  bal- 
ance using,  28-29. 

M 

Mahler    calorimeter,    description    of, 

use  of,  91. 
Marks    and    Davis,    latent    heat   of 

evaporation  according  to,  15. 


INDEX 


173 


Mercury,  use  of  in  nitrogen  deter- 
mination, 89. 

Methane,  in  flue  gas,  21. 

calorific  value  of ,  21 ;  effect  upon  the 
value  obtained  for  nitrogen,  146. 

Method, 

Eschka,  for  sulphur,  83;  Kjeldahl, 
for  nitrogen,  89. 

Methods  of  analysis,  79-90. 

Mines,  Bureau  of,  63,  125,  159. 

Moisture  in  air,  effect  on  heat  bal- 
ance, 22. 

Moisture  in  coal,  1,  43. 

amount  of,  2,  48;  losses  in  sam- 
pling, 75;  method  of  determining, 
79;  oven  for  determining,  80. 

Molecular  volume, 

definition  of,  141;  use  of,  in  gas 
reactions,  141-146. 

N 

Naphthalene,  calorific  value  of,  106. 
Nitrogen, 

amount  in  certain  coals,  47;  deter- 
mination of,  88;  effect  on  calcula- 
tion of  excess  air,  18;  in  flue  gases, 
132. 

in  the  Orsat  determination,  effect 
of  carbon  monoxide  upon,  144; 
of  high  available  hydrogen  upon, 
144;  of  methane  upon,  146;  of 
sulphur  upon,  144;  of  unburned 
hydrogen  upon,  145. 
specific  heat  of,  24. 


Ohio  Geological  Survey, 

Bulletin  No.  9  of,  10,  39,  41,  124, 

159;   sample  cans  used  by,  61. 
Ohio  No.  6  coal, 

calculation    of    available    heating 

power  of,  25;    composition  of,  25; 

products  of  complete  combustion 

of,  141-143. 
Ohio  State  University, 

heat  balance  calculations  at,  33; 

sampling  outfit  used  at,  63. 


Ohm's  law,  104. 

Orsat  determination, 

description  of,  134-137;  errors  in, 
147. 

Orsat  results, 

discussion  of,    141-149; 
effect  of  carbon  monoxide  on,  144; 
of  excess  air  on,  144;  of  hydrogen 
on,  146;  of  methane  on,  146;  of 
water  vapor  on,  143. 

Orsat's  apparatus,  134, 

care  of,  140;  drawing  sample  into, 
136;  figure  of,  135;  filling  of,  139; 
operation  of,  134;  reagents  for,  138. 

Oven, 

for  drying  coarse  samples,  71;  for 
moisture  determinations,  80. 

Oxygen, 

absorption  of,  by  pyrogallic  acid, 
140;  amount  of,  in  certain  coals, 
48;  determination  of,  in  coal,  90; 
determination  of,  in  flue  gas,  137; 
distribution  of,  in  coal,  11;  for 
calorimeter  work,  impurities  in, 
117;  in  excess  air,  16;  specific 
heat  of,  24. 


Peat,  composition  of,  158. 

Phosphorus,  determination  of,  in  coal, 
89. 

Potassium  hydroxide  solution, 

absorbing  power  of,  139;  for  Orsat 
apparatus,  138;  for  ultimate  anal- 
ysis, 88. 

Products  of  combustion,  15. 

sensible  heats  of,  31,  32;  specific 
heats  of,  23. 

Proximate  analysis  of  coal,  43-45. 

Purchase  of  coal  under  specifications, 
126-131. 

advantages  and  disadvantages  of, 
127. 

Pyrite, 

amounts  in  coal,  6;  composition 
of,  7,  8;  distribution  of,  in  coal, 
8;  effects  of,  on  accuracy  of  sam- 


174 


INDEX 


pling  coal,  66;  effects  of,  on  ash  of 
coal,  8;  heating  value  of,  7;  in 
unwashed  coal,  122;  in  washed 
coal,  124-125. 

Pyrogallic  acid,  solution  of,  138. 
absorbing  power  of,  140. 

R 

Radiation  correction,  in  calorimeter 

determination,  94. 
Reagents, 

absorbing  power  of,  139;    for  gas 

analysis,  138;   preparation  of,  138. 
Records,  summary  of  chemical,  119. 
Residual  coal,  38,  51. 

heating  value  of,  39. 
Resistance, 

for    reducing    voltage,     101;      of 

water,  102. 
Richards,    values  for  specific   heats 

according  to,  24. 


Sample  of  coal, 

air  dried,  119;  air  drying  of,  70; 
amount  of,  to  be  taken,  60,  64,  70; 
apparatus  for  reducing  amount  of, 
66,  72,  73;  as  received,  120;  cans 
for,  61,  63;  effect  of  clean  coal 
upon,  69;  effect  of  slate  and  pyrites 
upon,  66;  fineness  of,  74;  grinding 
of,  71,  74,  76;  method  of  taking, 
car,  63,  70;  method  of  taking, 
mine,  59;  reduction  of,  64,  71,  72, 
73. 

Sample  of  gas, 

alteration    of,    by    absorption    in 
water,    151-153;     by    chemical 
changes,  150;   by  leakage,  149. 
analysis  of,  132-137;  collection  of, 
132. 

Samplers,  mechanical,  66,  73. 

Samples  of  coal, 

alteration  of  fine,  76;  equipment 
for  reduction  of,  76;  mixing  of, 
79;  oxidation  of  fine,  76;  weighing 
out  of,  79. 


Sampling,  57-78. 

cars  of  coal,  63;  coal  as  used,  63; 
coal  containing  much  moisture,  74; 
coal  in  the  mine,  59-60;  errors  in, 
57-58,  66,  69;  outfit,  portable, 
61-62;  tubes  for  gases,  133. 

Silica,  in  coal  ash,  4. 

Silicates,  fusibility  of,  5. 

Slack  coal, 
moisture  in,  2. 

Smoke,  heat  loss  due  to,  22. 

Solution, 

acid,  cuprous  chloride,  138;  am- 
monia, 89,  95;  calcium  chloride, 
124;  cuprous  ammonium  chloride, 
138;  for  washing  coal,  124;  potas- 
sium hydroxide,  88,  138;  sodium 
hydroxide,  89;  sulphuric  acid,  89; 
zinc  chloride,  124. 

Soot,  heat  loss  due  to,  22. 

Specifications  for  purchase  of  coal,  128. 
abstracts  of,  for  certain  cities,  129- 
131;  of  U.  S.  Government,  131. 

Specific  gravity  of  coal,  122. 

of  solutions  for  washing  coal,  122. 

Specific  heat, 

of  gases,  23-24;  of  water,  114. 

Standard, 

materials,  106;  solution  of  am- 
monia, 89,  95;  solution  of  sul- 
phuric acid,  89;  thermometers,  109. 

Standards,  Bureau  of,  106,  110,  111. 

Sulphate,  ferrous  in  coal,  7. 
heating  value  of,  7. 

Sulphur  dioxide,  8. 
in  flue  gas,  143. 

Sulphuric  acid, 

in  desiccators,  81;  correction  for  in 
calorimeter  work,  100;  standard, 
89. 

Sulphur  in  coal, 

amount  of,  6,  100;  determination 
of,  83;  effect  of,  on  clinkering  of 
ash,  8;  forms  of,  6;  heating  value 
of,  7;  in  weathered  coal,  7;  organic, 
6;  removal  by  washing,  122. 

Sulphur  in  coke,  49. 

Sulphur  in  volatile  matter,  49. 


INDEX 


175 


Survey, 

Ohio  Geological,  Bulletin  No.  9  of, 
10,  39,  41,  124, 159;  sample  cans 
used  by,  61;  washing  tests  from, 
124. 

U.  S.  Geological,  Bulletin  No.  290 
of,  45,  159;  Bulletin  No.  332 
of,  159;  Professional  Paper  No. 
48  of,  45,  159. 


Table, 

of  corrections  for  stem  temperature, 
112;  of  density  of  water,  98;  of 
solubilities  of  gases,  151;  of  specific 
heats  of  gases,  24;  of  specific  heat 
of  water,  114;  of  thermal  capacity 
of  gases,  30;  of  thermal  capacity 
of  water,  114. 

Temperature, 

changes,  effects  on  Orsat  results, 
147-148;  conditions  in  calorimeter 
work,  98;  correction  for  stem  of 
thermometer,  110;  final  in  calor- 
imeter work,  93;  initial  in  calor- 
imeter work,  93. 

Thermal  capacity, 

definition  of,  27;  of  gases,  30;  of 
water,  114. 

Thermometers, 

calibration  of,  107;  comparison  of, 
110;  correction  to  reading,  107-1 12; 
errors  in  graduation  of,  107; 
standard,  109;  stem  temperature 
correction  for,  110;  stem  tempera- 
ture correction,  tabulation  of,  112. 

Total  heating  value  of  coal,  9. 

Tubes,  for  sampling  gas,  133. 

U 

Ultimate  analysis,  51. 
accuracy  of,  52;  calculation  of,  54; 
calculation  of  calorific  value  from, 
10;  determination  of,  85;  effect  of 
errors  in,  on  heat  balance,  56;  of 
certain  coals,  53. 


United  States, 

Bureau  of  Mines,  63,  125,  159; 
Bureau  of  Standards,  106, 110,  111; 
composition  of  coals  of,  159-168; 
Geological  Survey,  45,  159;  Gov- 
ernment purchase  of  coal  by,  131. 


Vacuum  flask,  109. 

Value  of  coal, 

basis  for  determining  comparative, 
126,  128;  British  thermal  value, 
9;  calorific  value,  9;  factors  affect- 
ing, 126. 

Volatile  matter, 

amount  in  certain  coals,  49;  com- 
position of,  49;  determination  of, 
82;  heating  value  of,  50. 

Voltage, 

desirable  in  calorimeter  work,  100; 
reduction  of,  by  shunt,  101. 

W 

Washing  coal, 

improvement  of  by,  122-125;  labor- 
atory equipment  for,  123;  results 
of,  124. 

Water, 

combined  in  clay,  4;  combined  in 
coals,  48;  density  of,  98;  effect  of, 
on  available  heating  power,  22; 
equivalent  of  calorimeter,  105; 
measuring  of,  in  calorimeter  work, 
97;  resistance  of,  102;  seal,  effects 
of,  on  gas  samples,  156;  surround- 
ing calorimeter  bomb,  97;  total  in 
coals,  48;  vapor,  effect  of,  on  gas 
analysis,  143;  vapor,  latent  heat  of, 
14;  vapor,  specific  heat  of,  24. 

Weathered  coal,  VII. 
sulphur  in,  7. 

Weighing  out  samples,  79. 

Wire, 

fuse  used  in  calorimeter  deter- 
mination, 95;  high  resistance,  101. 

Wood,  composition  of,  158. 


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